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Super Duper Vdd stiffening required on 555 timer, what is the best way?
Choosing resistor values for a 555 timerTriggering a 555 timer ICShould a 555 IC remain powered when a [battery powered] device is turned off?Control Output Shock From Cockroft-Walton DoublerGeneral circuit debugging techniques, and my 555 timer in particular555 auto-off timer circuit validityIs there anything wrong with this particular timer circuit utilizing 555?Controlling spotwelder timer with 555
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$begingroup$
I am using a 555 timer for a (16bit) frequency sensor/counter.
It works by counting the number of pulses read in the 125ms sample time set by a 555 timer; resets & repeats...
I am using the timer in astable operation.
TH (time pulse high) is the sampling ON signal.
This time is set and trimmed (+/- 5% adjustment range) with a high quality POT.
TL (time pulse
low) falling edge initiates a data-latch read --> then a counter reset operation
Right now I have it on a bread board. I am making a PCB for the final design and I want to iron out the following problem for the PCB design.
Here is the problem:
The measured frequency is not super stable (+/- ~3Hz @ 25kHz) and it takes a while to settle.
I think it is because the sample time is getting affected by the noise on the Vdd rail. I have decoupling caps on all the IC's but it is on a bread board so this can be expected.
For the PCB layout I want to insure the 555 timer is on a solid 5v and the DCDC converter output is steady.
Here are some ideas I have on how to do this.
- Use a rail-rail opamp and 4v7 reference to regulate the Timer Vdd @ 4v7
- Use ferrite beads to further decouple the Timer and all the other ICs from each other.
- Use a seperate DCDC converter for the timer.
- Use a linear regulator IC for the Timer Vdd.
Which of these would be the best practice for insuring a constant timer Vdd value?
pcb-design noise 555 decoupling-capacitor
edited Aug 13 at 16:30
Neil_UK
86.3k2 gold badges88 silver badges201 bronze badges
asked Aug 12 at 13:20
TonyTony
3651 silver badge11 bronze badges
$endgroup$
add a comment |
$begingroup$
I am using a 555 timer for a (16bit) frequency sensor/counter.
It works by counting the number of pulses read in the 125ms sample time set by a 555 timer; resets & repeats...
I am using the timer in astable operation.
TH (time pulse high) is the sampling ON signal.
This time is set and trimmed (+/- 5% adjustment range) with a high quality POT.
TL (time pulse
low) falling edge initiates a data-latch read --> then a counter reset operation
Right now I have it on a bread board. I am making a PCB for the final design and I want to iron out the following problem for the PCB design.
Here is the problem:
The measured frequency is not super stable (+/- ~3Hz @ 25kHz) and it takes a while to settle.
I think it is because the sample time is getting affected by the noise on the Vdd rail. I have decoupling caps on all the IC's but it is on a bread board so this can be expected.
For the PCB layout I want to insure the 555 timer is on a solid 5v and the DCDC converter output is steady.
Here are some ideas I have on how to do this.
- Use a rail-rail opamp and 4v7 reference to regulate the Timer Vdd @ 4v7
- Use ferrite beads to further decouple the Timer and all the other ICs from each other.
- Use a seperate DCDC converter for the timer.
- Use a linear regulator IC for the Timer Vdd.
Which of these would be the best practice for insuring a constant timer Vdd value?
pcb-design noise 555 decoupling-capacitor
edited Aug 13 at 16:30
Neil_UK
86.3k2 gold badges88 silver badges201 bronze badges
asked Aug 12 at 13:20
TonyTony
3651 silver badge11 bronze badges
$endgroup$
17
$begingroup$
Maybe you should use a crystal instead. I am actually impressed that it's only +/- 3Hz @ 25 kHz. That's great, considering you're using a 555 timer.
$endgroup$
– Harry Svensson
Aug 12 at 13:25
3
$begingroup$
VDD stiffening may not help : it may be some thermal effect (capacitor or the chip itself warming up). indeed, "takes some time to settle" suggests that. The other answers are absolutely correct : if 3Hz in 25kHz isn't good enough, you really want a fundamentally better source (e.g. watch crystal oscillator at 32.768 kHz.
$endgroup$
– Brian Drummond
Aug 12 at 21:59
1
$begingroup$
Awesome, I feel a lot better now about my circuit after finding out I'm getting pretty good results despite using a 555 timer as the reference. rev.2 will use a crystal and a counter to set the sample time. I can also adjust the sample time range by selecting which counter bit to use!
$endgroup$
– Tony
Aug 13 at 0:53
add a comment |
$begingroup$
I am using a 555 timer for a (16bit) frequency sensor/counter.
It works by counting the number of pulses read in the 125ms sample time set by a 555 timer; resets & repeats...
I am using the timer in astable operation.
TH (time pulse high) is the sampling ON signal.
This time is set and trimmed (+/- 5% adjustment range) with a high quality POT.
TL (time pulse
low) falling edge initiates a data-latch read --> then a counter reset operation
Right now I have it on a bread board. I am making a PCB for the final design and I want to iron out the following problem for the PCB design.
Here is the problem:
The measured frequency is not super stable (+/- ~3Hz @ 25kHz) and it takes a while to settle.
I think it is because the sample time is getting affected by the noise on the Vdd rail. I have decoupling caps on all the IC's but it is on a bread board so this can be expected.
For the PCB layout I want to insure the 555 timer is on a solid 5v and the DCDC converter output is steady.
Here are some ideas I have on how to do this.
- Use a rail-rail opamp and 4v7 reference to regulate the Timer Vdd @ 4v7
- Use ferrite beads to further decouple the Timer and all the other ICs from each other.
- Use a seperate DCDC converter for the timer.
- Use a linear regulator IC for the Timer Vdd.
Which of these would be the best practice for insuring a constant timer Vdd value?
pcb-design noise 555 decoupling-capacitor
edited Aug 13 at 16:30
Neil_UK
86.3k2 gold badges88 silver badges201 bronze badges
asked Aug 12 at 13:20
TonyTony
3651 silver badge11 bronze badges
$endgroup$
I am using a 555 timer for a (16bit) frequency sensor/counter.
It works by counting the number of pulses read in the 125ms sample time set by a 555 timer; resets & repeats...
I am using the timer in astable operation.
TH (time pulse high) is the sampling ON signal.
This time is set and trimmed (+/- 5% adjustment range) with a high quality POT.
TL (time pulse
low) falling edge initiates a data-latch read --> then a counter reset operation
Right now I have it on a bread board. I am making a PCB for the final design and I want to iron out the following problem for the PCB design.
Here is the problem:
The measured frequency is not super stable (+/- ~3Hz @ 25kHz) and it takes a while to settle.
I think it is because the sample time is getting affected by the noise on the Vdd rail. I have decoupling caps on all the IC's but it is on a bread board so this can be expected.
For the PCB layout I want to insure the 555 timer is on a solid 5v and the DCDC converter output is steady.
Here are some ideas I have on how to do this.
- Use a rail-rail opamp and 4v7 reference to regulate the Timer Vdd @ 4v7
- Use ferrite beads to further decouple the Timer and all the other ICs from each other.
- Use a seperate DCDC converter for the timer.
- Use a linear regulator IC for the Timer Vdd.
Which of these would be the best practice for insuring a constant timer Vdd value?
pcb-design noise 555 decoupling-capacitor
pcb-design noise 555 decoupling-capacitor
edited Aug 13 at 16:30
Neil_UK
86.3k2 gold badges88 silver badges201 bronze badges
asked Aug 12 at 13:20
TonyTony
3651 silver badge11 bronze badges
edited Aug 13 at 16:30
Neil_UK
86.3k2 gold badges88 silver badges201 bronze badges
asked Aug 12 at 13:20
TonyTony
3651 silver badge11 bronze badges
edited Aug 13 at 16:30
Neil_UK
86.3k2 gold badges88 silver badges201 bronze badges
edited Aug 13 at 16:30
Neil_UK
86.3k2 gold badges88 silver badges201 bronze badges
edited Aug 13 at 16:30
Neil_UK
86.3k2 gold badges88 silver badges201 bronze badges
86.3k2 gold badges88 silver badges201 bronze badges
asked Aug 12 at 13:20
TonyTony
3651 silver badge11 bronze badges
asked Aug 12 at 13:20
TonyTony
3651 silver badge11 bronze badges
asked Aug 12 at 13:20
TonyTony
3651 silver badge11 bronze badges
3651 silver badge11 bronze badges
17
$begingroup$
Maybe you should use a crystal instead. I am actually impressed that it's only +/- 3Hz @ 25 kHz. That's great, considering you're using a 555 timer.
$endgroup$
– Harry Svensson
Aug 12 at 13:25
3
$begingroup$
VDD stiffening may not help : it may be some thermal effect (capacitor or the chip itself warming up). indeed, "takes some time to settle" suggests that. The other answers are absolutely correct : if 3Hz in 25kHz isn't good enough, you really want a fundamentally better source (e.g. watch crystal oscillator at 32.768 kHz.
$endgroup$
– Brian Drummond
Aug 12 at 21:59
1
$begingroup$
Awesome, I feel a lot better now about my circuit after finding out I'm getting pretty good results despite using a 555 timer as the reference. rev.2 will use a crystal and a counter to set the sample time. I can also adjust the sample time range by selecting which counter bit to use!
$endgroup$
– Tony
Aug 13 at 0:53
add a comment |
17
$begingroup$
Maybe you should use a crystal instead. I am actually impressed that it's only +/- 3Hz @ 25 kHz. That's great, considering you're using a 555 timer.
$endgroup$
– Harry Svensson
Aug 12 at 13:25
3
$begingroup$
VDD stiffening may not help : it may be some thermal effect (capacitor or the chip itself warming up). indeed, "takes some time to settle" suggests that. The other answers are absolutely correct : if 3Hz in 25kHz isn't good enough, you really want a fundamentally better source (e.g. watch crystal oscillator at 32.768 kHz.
$endgroup$
– Brian Drummond
Aug 12 at 21:59
1
$begingroup$
Awesome, I feel a lot better now about my circuit after finding out I'm getting pretty good results despite using a 555 timer as the reference. rev.2 will use a crystal and a counter to set the sample time. I can also adjust the sample time range by selecting which counter bit to use!
$endgroup$
– Tony
Aug 13 at 0:53
17
17
$begingroup$
Maybe you should use a crystal instead. I am actually impressed that it's only +/- 3Hz @ 25 kHz. That's great, considering you're using a 555 timer.
$endgroup$
– Harry Svensson
Aug 12 at 13:25
$begingroup$
Maybe you should use a crystal instead. I am actually impressed that it's only +/- 3Hz @ 25 kHz. That's great, considering you're using a 555 timer.
$endgroup$
– Harry Svensson
Aug 12 at 13:25
3
3
$begingroup$
VDD stiffening may not help : it may be some thermal effect (capacitor or the chip itself warming up). indeed, "takes some time to settle" suggests that. The other answers are absolutely correct : if 3Hz in 25kHz isn't good enough, you really want a fundamentally better source (e.g. watch crystal oscillator at 32.768 kHz.
$endgroup$
– Brian Drummond
Aug 12 at 21:59
$begingroup$
VDD stiffening may not help : it may be some thermal effect (capacitor or the chip itself warming up). indeed, "takes some time to settle" suggests that. The other answers are absolutely correct : if 3Hz in 25kHz isn't good enough, you really want a fundamentally better source (e.g. watch crystal oscillator at 32.768 kHz.
$endgroup$
– Brian Drummond
Aug 12 at 21:59
1
1
$begingroup$
Awesome, I feel a lot better now about my circuit after finding out I'm getting pretty good results despite using a 555 timer as the reference. rev.2 will use a crystal and a counter to set the sample time. I can also adjust the sample time range by selecting which counter bit to use!
$endgroup$
– Tony
Aug 13 at 0:53
$begingroup$
Awesome, I feel a lot better now about my circuit after finding out I'm getting pretty good results despite using a 555 timer as the reference. rev.2 will use a crystal and a counter to set the sample time. I can also adjust the sample time range by selecting which counter bit to use!
$endgroup$
– Tony
Aug 13 at 0:53
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer.
You can improve it by using low temperature coefficient resistors and capacitors in the timing circuit, maybe by bypassing pin 5 to ground, by isolating the circuit thermally and electrically, in the extreme controlling the temperature in an oven, powering it from a battery with an ultra-low noise linear regulator and capacitance multiplier stage, and using opto-isolation on the outputs.
But that's just silly. Use a crystal, they're cheap and orders of magnitude better. For example, a 100kHz crystal, oscillator (74HCU04 + a couple resistors + load caps) and a divide-by-four (eg. a 74HC74). Tolerance (absolute accuracy) of that particular linked crystal is +/-30ppm or about 0.75Hz in 25kHz. Short term stability will be much better again.
There are also programmable oscillator products you can order, there might be one in a useful range for you.
answered Aug 12 at 13:38
Spehro PefhanySpehro Pefhany
222k5 gold badges177 silver badges464 bronze badges
$endgroup$
$begingroup$
"Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer." - How would one compensate it to make it more stable?
$endgroup$
– Harry Svensson
Aug 12 at 14:30
6
$begingroup$
@HarrySvensson You could isolate it from thermal effects like air currents and introduce deliberately temperature sensitive components to compensate for the drift of the capacitor and resistors (and, to a lesser extent, the IC). If crystals (and ceramic resonators) were not so cheap and available, such techniques might make sense. Another method is to use a lookup table driven by temperature, stored in EEPROM to trim some parameter.
$endgroup$
– Spehro Pefhany
Aug 12 at 14:35
1
$begingroup$
Better than a 100kHz crystal and 74HCU04, a 74HC4060 and a 6.4MHz crystal. Take your clock off of Q8, and Bob's yer uncle.
$endgroup$
– TimWescott
Aug 13 at 1:02
$begingroup$
@TimWescott good option, can use a rugged HC49 crystal too, with higher maximum drive.
$endgroup$
– Spehro Pefhany
Aug 13 at 1:15
add a comment |
$begingroup$
I don't think you will ever get the accuracy and stability you want from a 555 timer. The pulse width is determined by the values of resistors and a capacitor, and the values of these elements will change with temperature and over time.
For a precise pulse duration you should be looking at a crystal oscillator with a digital counter to generate the desired pulse.
answered Aug 12 at 13:25
Elliot AldersonElliot Alderson
11.7k2 gold badges12 silver badges25 bronze badges
$endgroup$
add a comment |
$begingroup$
While I have many fond memories of using a 555 timer, sadly, incredibly cheap microcontrollers with a crystal are almost always a better choice for timers nowadays.
The PIC16 series has some members which have a very wide voltage range (3.3-18V+) and are available for a dollar and change.
answered Aug 21 at 7:13
Andrew LentvorskiAndrew Lentvorski
462 bronze badges
New contributor
Andrew Lentvorski is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
1
$begingroup$
Agreed, but I try hard not to use MCU's when I don't have to. I make IC tester boards. This is like a handy peripherally circuit that I can just copy and paste into new designs without having to flash program anything. Its so I don't need to use up a large expensive oscilloscope just to measure frequency.
$endgroup$
– Tony
Aug 22 at 0:04
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer.
You can improve it by using low temperature coefficient resistors and capacitors in the timing circuit, maybe by bypassing pin 5 to ground, by isolating the circuit thermally and electrically, in the extreme controlling the temperature in an oven, powering it from a battery with an ultra-low noise linear regulator and capacitance multiplier stage, and using opto-isolation on the outputs.
But that's just silly. Use a crystal, they're cheap and orders of magnitude better. For example, a 100kHz crystal, oscillator (74HCU04 + a couple resistors + load caps) and a divide-by-four (eg. a 74HC74). Tolerance (absolute accuracy) of that particular linked crystal is +/-30ppm or about 0.75Hz in 25kHz. Short term stability will be much better again.
There are also programmable oscillator products you can order, there might be one in a useful range for you.
answered Aug 12 at 13:38
Spehro PefhanySpehro Pefhany
222k5 gold badges177 silver badges464 bronze badges
$endgroup$
$begingroup$
"Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer." - How would one compensate it to make it more stable?
$endgroup$
– Harry Svensson
Aug 12 at 14:30
6
$begingroup$
@HarrySvensson You could isolate it from thermal effects like air currents and introduce deliberately temperature sensitive components to compensate for the drift of the capacitor and resistors (and, to a lesser extent, the IC). If crystals (and ceramic resonators) were not so cheap and available, such techniques might make sense. Another method is to use a lookup table driven by temperature, stored in EEPROM to trim some parameter.
$endgroup$
– Spehro Pefhany
Aug 12 at 14:35
1
$begingroup$
Better than a 100kHz crystal and 74HCU04, a 74HC4060 and a 6.4MHz crystal. Take your clock off of Q8, and Bob's yer uncle.
$endgroup$
– TimWescott
Aug 13 at 1:02
$begingroup$
@TimWescott good option, can use a rugged HC49 crystal too, with higher maximum drive.
$endgroup$
– Spehro Pefhany
Aug 13 at 1:15
add a comment |
$begingroup$
Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer.
You can improve it by using low temperature coefficient resistors and capacitors in the timing circuit, maybe by bypassing pin 5 to ground, by isolating the circuit thermally and electrically, in the extreme controlling the temperature in an oven, powering it from a battery with an ultra-low noise linear regulator and capacitance multiplier stage, and using opto-isolation on the outputs.
But that's just silly. Use a crystal, they're cheap and orders of magnitude better. For example, a 100kHz crystal, oscillator (74HCU04 + a couple resistors + load caps) and a divide-by-four (eg. a 74HC74). Tolerance (absolute accuracy) of that particular linked crystal is +/-30ppm or about 0.75Hz in 25kHz. Short term stability will be much better again.
There are also programmable oscillator products you can order, there might be one in a useful range for you.
answered Aug 12 at 13:38
Spehro PefhanySpehro Pefhany
222k5 gold badges177 silver badges464 bronze badges
$endgroup$
$begingroup$
"Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer." - How would one compensate it to make it more stable?
$endgroup$
– Harry Svensson
Aug 12 at 14:30
6
$begingroup$
@HarrySvensson You could isolate it from thermal effects like air currents and introduce deliberately temperature sensitive components to compensate for the drift of the capacitor and resistors (and, to a lesser extent, the IC). If crystals (and ceramic resonators) were not so cheap and available, such techniques might make sense. Another method is to use a lookup table driven by temperature, stored in EEPROM to trim some parameter.
$endgroup$
– Spehro Pefhany
Aug 12 at 14:35
1
$begingroup$
Better than a 100kHz crystal and 74HCU04, a 74HC4060 and a 6.4MHz crystal. Take your clock off of Q8, and Bob's yer uncle.
$endgroup$
– TimWescott
Aug 13 at 1:02
$begingroup$
@TimWescott good option, can use a rugged HC49 crystal too, with higher maximum drive.
$endgroup$
– Spehro Pefhany
Aug 13 at 1:15
add a comment |
$begingroup$
Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer.
You can improve it by using low temperature coefficient resistors and capacitors in the timing circuit, maybe by bypassing pin 5 to ground, by isolating the circuit thermally and electrically, in the extreme controlling the temperature in an oven, powering it from a battery with an ultra-low noise linear regulator and capacitance multiplier stage, and using opto-isolation on the outputs.
But that's just silly. Use a crystal, they're cheap and orders of magnitude better. For example, a 100kHz crystal, oscillator (74HCU04 + a couple resistors + load caps) and a divide-by-four (eg. a 74HC74). Tolerance (absolute accuracy) of that particular linked crystal is +/-30ppm or about 0.75Hz in 25kHz. Short term stability will be much better again.
There are also programmable oscillator products you can order, there might be one in a useful range for you.
answered Aug 12 at 13:38
Spehro PefhanySpehro Pefhany
222k5 gold badges177 silver badges464 bronze badges
$endgroup$
Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer.
You can improve it by using low temperature coefficient resistors and capacitors in the timing circuit, maybe by bypassing pin 5 to ground, by isolating the circuit thermally and electrically, in the extreme controlling the temperature in an oven, powering it from a battery with an ultra-low noise linear regulator and capacitance multiplier stage, and using opto-isolation on the outputs.
But that's just silly. Use a crystal, they're cheap and orders of magnitude better. For example, a 100kHz crystal, oscillator (74HCU04 + a couple resistors + load caps) and a divide-by-four (eg. a 74HC74). Tolerance (absolute accuracy) of that particular linked crystal is +/-30ppm or about 0.75Hz in 25kHz. Short term stability will be much better again.
There are also programmable oscillator products you can order, there might be one in a useful range for you.
answered Aug 12 at 13:38
Spehro PefhanySpehro Pefhany
222k5 gold badges177 silver badges464 bronze badges
answered Aug 12 at 13:38
Spehro PefhanySpehro Pefhany
222k5 gold badges177 silver badges464 bronze badges
answered Aug 12 at 13:38
Spehro PefhanySpehro Pefhany
222k5 gold badges177 silver badges464 bronze badges
answered Aug 12 at 13:38
Spehro PefhanySpehro Pefhany
222k5 gold badges177 silver badges464 bronze badges
222k5 gold badges177 silver badges464 bronze badges
$begingroup$
"Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer." - How would one compensate it to make it more stable?
$endgroup$
– Harry Svensson
Aug 12 at 14:30
6
$begingroup$
@HarrySvensson You could isolate it from thermal effects like air currents and introduce deliberately temperature sensitive components to compensate for the drift of the capacitor and resistors (and, to a lesser extent, the IC). If crystals (and ceramic resonators) were not so cheap and available, such techniques might make sense. Another method is to use a lookup table driven by temperature, stored in EEPROM to trim some parameter.
$endgroup$
– Spehro Pefhany
Aug 12 at 14:35
1
$begingroup$
Better than a 100kHz crystal and 74HCU04, a 74HC4060 and a 6.4MHz crystal. Take your clock off of Q8, and Bob's yer uncle.
$endgroup$
– TimWescott
Aug 13 at 1:02
$begingroup$
@TimWescott good option, can use a rugged HC49 crystal too, with higher maximum drive.
$endgroup$
– Spehro Pefhany
Aug 13 at 1:15
add a comment |
$begingroup$
"Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer." - How would one compensate it to make it more stable?
$endgroup$
– Harry Svensson
Aug 12 at 14:30
6
$begingroup$
@HarrySvensson You could isolate it from thermal effects like air currents and introduce deliberately temperature sensitive components to compensate for the drift of the capacitor and resistors (and, to a lesser extent, the IC). If crystals (and ceramic resonators) were not so cheap and available, such techniques might make sense. Another method is to use a lookup table driven by temperature, stored in EEPROM to trim some parameter.
$endgroup$
– Spehro Pefhany
Aug 12 at 14:35
1
$begingroup$
Better than a 100kHz crystal and 74HCU04, a 74HC4060 and a 6.4MHz crystal. Take your clock off of Q8, and Bob's yer uncle.
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– TimWescott
Aug 13 at 1:02
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@TimWescott good option, can use a rugged HC49 crystal too, with higher maximum drive.
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– Spehro Pefhany
Aug 13 at 1:15
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"Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer." - How would one compensate it to make it more stable?
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– Harry Svensson
Aug 12 at 14:30
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"Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer." - How would one compensate it to make it more stable?
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– Harry Svensson
Aug 12 at 14:30
6
6
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@HarrySvensson You could isolate it from thermal effects like air currents and introduce deliberately temperature sensitive components to compensate for the drift of the capacitor and resistors (and, to a lesser extent, the IC). If crystals (and ceramic resonators) were not so cheap and available, such techniques might make sense. Another method is to use a lookup table driven by temperature, stored in EEPROM to trim some parameter.
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– Spehro Pefhany
Aug 12 at 14:35
$begingroup$
@HarrySvensson You could isolate it from thermal effects like air currents and introduce deliberately temperature sensitive components to compensate for the drift of the capacitor and resistors (and, to a lesser extent, the IC). If crystals (and ceramic resonators) were not so cheap and available, such techniques might make sense. Another method is to use a lookup table driven by temperature, stored in EEPROM to trim some parameter.
$endgroup$
– Spehro Pefhany
Aug 12 at 14:35
1
1
$begingroup$
Better than a 100kHz crystal and 74HCU04, a 74HC4060 and a 6.4MHz crystal. Take your clock off of Q8, and Bob's yer uncle.
$endgroup$
– TimWescott
Aug 13 at 1:02
$begingroup$
Better than a 100kHz crystal and 74HCU04, a 74HC4060 and a 6.4MHz crystal. Take your clock off of Q8, and Bob's yer uncle.
$endgroup$
– TimWescott
Aug 13 at 1:02
$begingroup$
@TimWescott good option, can use a rugged HC49 crystal too, with higher maximum drive.
$endgroup$
– Spehro Pefhany
Aug 13 at 1:15
$begingroup$
@TimWescott good option, can use a rugged HC49 crystal too, with higher maximum drive.
$endgroup$
– Spehro Pefhany
Aug 13 at 1:15
add a comment |
$begingroup$
I don't think you will ever get the accuracy and stability you want from a 555 timer. The pulse width is determined by the values of resistors and a capacitor, and the values of these elements will change with temperature and over time.
For a precise pulse duration you should be looking at a crystal oscillator with a digital counter to generate the desired pulse.
answered Aug 12 at 13:25
Elliot AldersonElliot Alderson
11.7k2 gold badges12 silver badges25 bronze badges
$endgroup$
add a comment |
$begingroup$
I don't think you will ever get the accuracy and stability you want from a 555 timer. The pulse width is determined by the values of resistors and a capacitor, and the values of these elements will change with temperature and over time.
For a precise pulse duration you should be looking at a crystal oscillator with a digital counter to generate the desired pulse.
answered Aug 12 at 13:25
Elliot AldersonElliot Alderson
11.7k2 gold badges12 silver badges25 bronze badges
$endgroup$
add a comment |
$begingroup$
I don't think you will ever get the accuracy and stability you want from a 555 timer. The pulse width is determined by the values of resistors and a capacitor, and the values of these elements will change with temperature and over time.
For a precise pulse duration you should be looking at a crystal oscillator with a digital counter to generate the desired pulse.
answered Aug 12 at 13:25
Elliot AldersonElliot Alderson
11.7k2 gold badges12 silver badges25 bronze badges
$endgroup$
I don't think you will ever get the accuracy and stability you want from a 555 timer. The pulse width is determined by the values of resistors and a capacitor, and the values of these elements will change with temperature and over time.
For a precise pulse duration you should be looking at a crystal oscillator with a digital counter to generate the desired pulse.
answered Aug 12 at 13:25
Elliot AldersonElliot Alderson
11.7k2 gold badges12 silver badges25 bronze badges
answered Aug 12 at 13:25
Elliot AldersonElliot Alderson
11.7k2 gold badges12 silver badges25 bronze badges
answered Aug 12 at 13:25
Elliot AldersonElliot Alderson
11.7k2 gold badges12 silver badges25 bronze badges
answered Aug 12 at 13:25
Elliot AldersonElliot Alderson
11.7k2 gold badges12 silver badges25 bronze badges
11.7k2 gold badges12 silver badges25 bronze badges
add a comment |
add a comment |
$begingroup$
While I have many fond memories of using a 555 timer, sadly, incredibly cheap microcontrollers with a crystal are almost always a better choice for timers nowadays.
The PIC16 series has some members which have a very wide voltage range (3.3-18V+) and are available for a dollar and change.
answered Aug 21 at 7:13
Andrew LentvorskiAndrew Lentvorski
462 bronze badges
New contributor
Andrew Lentvorski is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
1
$begingroup$
Agreed, but I try hard not to use MCU's when I don't have to. I make IC tester boards. This is like a handy peripherally circuit that I can just copy and paste into new designs without having to flash program anything. Its so I don't need to use up a large expensive oscilloscope just to measure frequency.
$endgroup$
– Tony
Aug 22 at 0:04
add a comment |
$begingroup$
While I have many fond memories of using a 555 timer, sadly, incredibly cheap microcontrollers with a crystal are almost always a better choice for timers nowadays.
The PIC16 series has some members which have a very wide voltage range (3.3-18V+) and are available for a dollar and change.
answered Aug 21 at 7:13
Andrew LentvorskiAndrew Lentvorski
462 bronze badges
New contributor
Andrew Lentvorski is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
1
$begingroup$
Agreed, but I try hard not to use MCU's when I don't have to. I make IC tester boards. This is like a handy peripherally circuit that I can just copy and paste into new designs without having to flash program anything. Its so I don't need to use up a large expensive oscilloscope just to measure frequency.
$endgroup$
– Tony
Aug 22 at 0:04
add a comment |
$begingroup$
While I have many fond memories of using a 555 timer, sadly, incredibly cheap microcontrollers with a crystal are almost always a better choice for timers nowadays.
The PIC16 series has some members which have a very wide voltage range (3.3-18V+) and are available for a dollar and change.
answered Aug 21 at 7:13
Andrew LentvorskiAndrew Lentvorski
462 bronze badges
New contributor
Andrew Lentvorski is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
While I have many fond memories of using a 555 timer, sadly, incredibly cheap microcontrollers with a crystal are almost always a better choice for timers nowadays.
The PIC16 series has some members which have a very wide voltage range (3.3-18V+) and are available for a dollar and change.
answered Aug 21 at 7:13
Andrew LentvorskiAndrew Lentvorski
462 bronze badges
New contributor
Andrew Lentvorski is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered Aug 21 at 7:13
Andrew LentvorskiAndrew Lentvorski
462 bronze badges
New contributor
Andrew Lentvorski is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered Aug 21 at 7:13
Andrew LentvorskiAndrew Lentvorski
462 bronze badges
answered Aug 21 at 7:13
Andrew LentvorskiAndrew Lentvorski
462 bronze badges
462 bronze badges
New contributor
Andrew Lentvorski is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Andrew Lentvorski is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
$begingroup$
Agreed, but I try hard not to use MCU's when I don't have to. I make IC tester boards. This is like a handy peripherally circuit that I can just copy and paste into new designs without having to flash program anything. Its so I don't need to use up a large expensive oscilloscope just to measure frequency.
$endgroup$
– Tony
Aug 22 at 0:04
add a comment |
1
$begingroup$
Agreed, but I try hard not to use MCU's when I don't have to. I make IC tester boards. This is like a handy peripherally circuit that I can just copy and paste into new designs without having to flash program anything. Its so I don't need to use up a large expensive oscilloscope just to measure frequency.
$endgroup$
– Tony
Aug 22 at 0:04
1
1
$begingroup$
Agreed, but I try hard not to use MCU's when I don't have to. I make IC tester boards. This is like a handy peripherally circuit that I can just copy and paste into new designs without having to flash program anything. Its so I don't need to use up a large expensive oscilloscope just to measure frequency.
$endgroup$
– Tony
Aug 22 at 0:04
$begingroup$
Agreed, but I try hard not to use MCU's when I don't have to. I make IC tester boards. This is like a handy peripherally circuit that I can just copy and paste into new designs without having to flash program anything. Its so I don't need to use up a large expensive oscilloscope just to measure frequency.
$endgroup$
– Tony
Aug 22 at 0:04
add a comment |
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$begingroup$
Maybe you should use a crystal instead. I am actually impressed that it's only +/- 3Hz @ 25 kHz. That's great, considering you're using a 555 timer.
$endgroup$
– Harry Svensson
Aug 12 at 13:25
3
$begingroup$
VDD stiffening may not help : it may be some thermal effect (capacitor or the chip itself warming up). indeed, "takes some time to settle" suggests that. The other answers are absolutely correct : if 3Hz in 25kHz isn't good enough, you really want a fundamentally better source (e.g. watch crystal oscillator at 32.768 kHz.
$endgroup$
– Brian Drummond
Aug 12 at 21:59
1
$begingroup$
Awesome, I feel a lot better now about my circuit after finding out I'm getting pretty good results despite using a 555 timer as the reference. rev.2 will use a crystal and a counter to set the sample time. I can also adjust the sample time range by selecting which counter bit to use!
$endgroup$
– Tony
Aug 13 at 0:53