I'm on a quest here. I am trying to find a circuit with a 555 timer that can both independently control the frequency and duty cycle(1% to 99%). Most circuit I find is either or, A few was actually what I thought i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa. I know with a LM393, (and I have that circuit) it is possible. but it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us while the lm393 starts about at 100us thanks for the help
but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.
fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us while the lm393 starts about at 100us
Use the 555 (ugh!) to make a triangle wave of constant amplitude and variable frequency. Then use a comparator to turn that into a variable duty cycle.
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John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.
fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us while the lm393 starts about at 100us
Since you seem to be operating at relatively high frequencies, you could alter the duty cycle with a pot and diodes and use a variable capacitor to change the frequency.
You could also do it with a microcontroller with appropriate peripherals on-chip (ADC inputs and a suitable timing peripheral)
y control the frequency and duty cycle(1% to 99%).
eded but when completing the circuit, I found that when varying the frequen cy.. the duty cycle was also changing !! or vice versa.
not fast enough. I can see on the scope that the 555 pulse starts to deteri orates 2.5us while the lm393 starts about at 100us
HI,
With further testing today I found that with Pic chip i was able to get bet ter rise and fall time. I am not looking for high frequency, just fast rise time. The Pic chip starts to deteriorate at 2.5us and the 555 chip at 50u s... now i'm thinking maybe there is something else faster then that !!
but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.
fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us while the lm393 starts about at 100us
rise and fall time. I am not looking for high frequency, just fast rise time. The Pic chip starts to deteriorate at 2.5us and the 555 chip at 50us... now i'm thinking maybe there is something else faster then that !!
The edges out of a pic should be nanoseconds, not microseconds. Is your scope OK?
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John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.
fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us while the lm393 starts about at 100us
Are you looking for voltage control, or via a potentiometer, or what?
Maximum frequency of operation? Slicing via a comparator can easily give you the independent duty cycle but may not be adequate at very narrow slivers if your frequency is high. ...Jim Thompson
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| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
When you personally applied this part to the task, how did you manage the reliable 1% and 99% duty factors with low jitter? And how did you compensate for the delay through the part?
I used to design pulse/function generators for a living, so be as technical as necessary.
Damn! I almost suffocated on the Chardonnay that went up my nose when I started laughing >:-} ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
y control the frequency and duty cycle(1% to 99%).
eded but when completing the circuit, I found that when varying the frequen cy.. the duty cycle was also changing !! or vice versa.
not fast enough. I can see on the scope that the 555 pulse starts to deteri orates 2.5us while the lm393 starts about at 100us This is an ill-conceived quest. If you want independent control of frequenc y and duty cycle, use a pair of counters, one dividing a high frequency clo ck - to determine your repetition frequency - from (say) falling edge to fa lling edge - and the other to determine where the intervening (say) rising edge appears.
If you used a 200MHz clock generator (which you can buy, off the shelf - Fa rnell has eleven in stock, several of them for about $A10 each in small qua ntities) and a pair of 20-bit counters in programmable logic device you'd b e able to get down to 200Hz.
You'd have to limit your maximum frequency to 2MHz to be able to have a 1%/
99% range on duty cycle would limit your maximum frequency to 20MHz, but th e edge speeds would be fine.
If you went for ECLinPS counters, you could use the MC100EP195 delay genera tor to get finer positioning of the intermediate edge.
formatting link
That provides up to 10nsec of delay, allowing you to drop back to a 100MHz oscillator programmable in roughly 10psec increments. The delay is depressi ngly temperature dependent (see figure 4) but if you were serious you could set up and auto-calibration procedure where you set up a fast repetition r ate waveform and measure it's DC contents as a function of the mark-to-spac e ratio set up by the delays in the MC100EP195. You'd need a 12-bit A/D co nverter or better, and a decent low pass filter in front of it but there's nothing complicated involved, and you can re-calibrate in few tens of milli seconds if you do it right.
needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.
fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us while the lm393 starts about at 100us
rise and fall time. I am not looking for high frequency, just fast rise time. The Pic chip starts to deteriorate at 2.5us and the 555 chip at 50us... now i'm thinking maybe there is something else faster then that !!
If one were to load it directly with a reasonably hefty MOSFET gate, it could easily degrade to microseconds. Maybe 100-200nC would do it.
A driver circuit (a couple BJTs or a chip) would take care of it, were that to be the case.
Best regards, Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
y control the frequency and duty cycle(1% to 99%).
I refer you to the "IC Timer Cookbook", copyright 1977 Walter G. Jung, Howard W. Sam's Publishing, cat# 21416, ISBN 0-672-21416-4 - Section
5.9.1, page 128. Another hint - it's done with diodes (resistors charge/discharge the timing caps through different paths). Hint 3 - quoting from page 130 "A very interesting version of this circuit results when the timing resistances, Rta and Rtb, are made the center- to-end resistances of a single potentiometer. With the arm of the potentiometer centered, Rta=Rtb, so the duty cycle will be 50% producing square waves. As the arm is varied to either side of center, Rta increases as Rtb decreases (or vice-versa), but the total resistance remains the same. As a result, the duty cycle can be varied while the frequency remains the same."
Speaking of mentoring, this was posted recently to my LinkedIn profile by a person I can't even remember working with....
[snip] "I have had the pleasure of working on and off with Jim since 1989 at Honeywell and also as a contractor. Jim is one of the most creative inventors and truly one of the early pioneers of many famous circuits. I learned a great deal from Jim yet only scratched the surface of his knowledge. Jim is also a real kick to talk to and work with great people skills. Jim has probably the most experience, noted by his many accomplishments, of any designer I know. I've known a lot. Jim is a great asset to have as he will always come up with something elegant, making you think, ?Now why didn't I think of that, it was right under my nose?? I highly recommend Jim and would gladly work with him in the future." ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
The foregoing was a paid political announcement for "Jim Thompson for Class President."
;)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Nope. I've never been ELECTED to anything, for obvious reasons >:-}
The LinkedIn endorsement, which you can view in my profile, was posted by a "Brad Davis", who I cannot recall at all, but I haven't been near any Phoenix Honeywell locations for at least 18 years. I did do a chip design for Honeywell Sensors Division, Minneapolis, around 2 years ago... but there was no "Brad Davis" there.
I'm just tiring of being considered the ogre, when the real ogres are the likes of Jamie... just go back thru this thread.
I've also reached my limit on tolerating narcissistic ignorance, and will slap it down whenever it occurs, by whomever.
Another endorsement, by a fellow I do remember... we used to leave Honeywell for lunch (and a bottle of wine) at Red Lobster, then doodle circuit issues on their paper table "cloths" for two or three hours, before returning to Honeywell, received March 7, via E-mail:
"Hi Jim, How are you doing? I was just sitting here thinking about you. I do that often. Today I was just reminiscing over my career. I?ve got this young pup working with me who is really, really good. I keep thinking about how difficult this job is when you don?t have a mentor and that reminded me of you. I truly miss the days when you were my mentor. I felt like there wasn?t anything I couldn?t do. I learned a great amount from you. You?ve helped me through many tough times. I really wish I was still working with you. I don?t think I?m cut out to be the top dog. So, I?m just writing to say hello and thanks for all you gave me. Rxxxxxx X. Sxxxx P.S. Sorry I?m not a very elegant writer. Electromech Technologies
2600 S. Custer Wichita, KS 67217" ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.
fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us while the lm393 starts about at 100us
--
Indeed, but not always for free.
I have a nice digital circuit which can keep the duty cycle of a
variable-frequency signal constant.
How much of your intellectual property have you ever given away?
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