How do I build a pulse generator?

Discussion in 'The Projects Forum' started by TheEquineFencer, May 26, 2013.

  1. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    I'm more of nuts and bolts type of guy. When I get an idea I try to figure out how to do it. When I find out how to build it, I do it. Then I bench test them, if they work I move on with it. I'm looking a 555 timer circuit that I can adjust the on/off time. I want to see if the SSR I'm looking at will hold up as the manufacturer says it will for what I want to do with it. Do you know where I can find a diagram for this? I want to power the 555 from a 12VDC source and trigger it from a 5VDC source. I want to generate a pulsed 5VDC signal that will operate the SSR in the 1s to as fast as a 2ms range. Max amp rating for the input needed is 12ma for the SSR. I'd like to be able to adjust the speed. I do own an oscilloscope and can figure out how to check the signals. An even on/off pulsed signal is what I'm looking for. If you can help or send me in the right direction it would be helpful. Thanks and keep up the good work on the website, it's an inspiration.
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Here's a schematic for a 555 astable multivibrator. You can change the pulse time by changing the values of R1, R2, and C1.
     
  3. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    Please explain a couple of things for me if you would. What you have marked as PH1 is just for the capacitors? Is this an adjustable Uf type pot or a real on/off type switch? R1and R2, I should be able to use a pot for those to make them adjustable, am I correct? What would happen if I adjusted the R1-R2 and did not adjust uF or vise/versa?
     
  4. tracecom

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    PH1 is a group of pin header pairs that are used to select C1; selection is done by shorting together the pair for the capacitor value desired. Changing R1 and R2 will also affect the pulse duration, but selecting the correct values is a little complicated. And yes, it's possible to use trimpots to make the time variable.

    If you know the range of time you need to cover, I should be able to calculate the RC values for that range.
     
  5. tracecom

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  6. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    In a perfect world, I'd like to be able to go from 1 second on/off to 2 milli-seconds on/off. If I had to narrow it down to smaller band, I'd say as fast as 2ms and a slow of 75ms. I'm thinking if I'm going to cook the SSR, it will do it at the faster pulsed rate. Thanks for helping.
     
  7. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    I saw some things like this when I've been doing a google search. I wonder if I can just change a few things on the board to get the faster switching time I need? I don't think I can mount it to this board, the SSR has a huge heat sink. I might be able to mount it on some riser post though. I like the idea. I think I'll see if I can contact that company and get some input into changing the board to operate at the speed I want. Looking at the picture they have, right off hand can you tell what I'd need to change to speed it up?
     
  8. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    The company that builds that timer has a website/forum. I'll post a message on there and see what I get. Thanks for the idea!
     
  9. tracecom

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    Apr 16, 2010
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    I have done some calculations, but it's late and I'm sleepy. If you don't get what you need from the Velleman forum, come back here for more help. BTW, the forum is based in the Netherlands and it's morning there, so this may be a good time to post. Post your question in the mini-kits forum.
     
  10. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    Thanks, that's where I'm at now, kit forums. Yes it is late. I see you are in West Tenn, I'm in Eastern,NC. I'm getting hungry too. You've been a lot of help, thanks.
     
    Last edited: May 26, 2013
  11. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    Here's what I've come up. This is the link to the timers I've ordrered.
    http://www.vellemanusa.com/downloads/0/minikits/manuals/manual_mk111.pdf
    It has a diagram for the circuit for the most part I will use.

    Here's a responce I got from a forum the company that builds the timer has.
    http://forum.velleman.eu/viewtopic.php?f=5&t=9158

    Experiment by using a lower value for C3 (100 uF now?).
    Lowering C3 will shorten pulse time and pause time.
    The MK111 does not have a 5 Volt output. If you want the output to be around 5 Volts, you should use a power supply of about 5 Volts.

    Question, what caps would you start with? My second plan is to install the SSR wired in place of the relay pictured in the OEM Diagram. I will use a 12VDC power source and then install a regulator to bring it down to 5VDC to power the 555 timer circuit.

    The SSR I've ordered is a DC60D20 made by Crydom. It was a pain to find someone that would order just 1 of them. Digikey wanted a min order of 20 at around $75 each. I lucked up and found http://octopart.com/ it's a search engine for parts like this. It listed several sources and two of them did not have a min order. I just hope I get the SSR soon. For the order of one, it said I had to split the order because the SSR was to be shipped straight from the builder to me. I also ordered the cover for the switch, they had that in stock.
     
  12. tracecom

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    I'll work on the value for C3; I am thinking 10 μF or less.

    I don't know why you want a 5V output from the 555; the SSR will work fine on 12 VDC.

    What are you planning to switch with the SSR?
     
    Last edited: May 26, 2013
  13. tracecom

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    I breadboarded the circuit and tried some different capacitor values for C3. With a .47 μF ceramic, I was able to get some decent square waves from 1 mS up to about 20 mS. A 1 μF will go up to about 50 mS, etc. Because the pot values are not optimized for these low capacitance values, it takes some fiddling with both pots to get a ≈50% duty cycle. I suggest that you be prepared to do some C3 substitutions in order to vary the pulse rate substantially. Of course, you can also vary the pot values if you want. Once you get the output waveform you want, you might want to replace the pots with fixed resistors of the right value.

    And if you are not using a relay (or some other inductive load) on the 555 output, you don't need D1.

    Good luck.
     
  14. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    Thanks for the input. I'll try it. I'm waiting for the parts and kit to get here now. I'm thinking of using someway to be able to install and remove the Caps until I get it right. Maybe remote mount them for the time being. the output will power a SSR, not the relay that comes with the kit.
     
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