want a Fixed 5% duty cycle, 12v input 50hz

Most selenoids I have work with are ON or OFF. Do you have a scope you can drop on it?

You should be able to do it with a 555 timers and FET, or a PIC and FET.. You are sure it is a selenoid? Do you know the frequency you want it send to it?

mramos1 said:

Most selenoids I have work with are ON or OFF. Do you have a scope you can drop on it?

You should be able to do it with a 555 timers and FET, or a PIC and FET.. You are sure it is a selenoid? Do you know the frequency you want it send to it?

Click to expand...

50hz. It goes on and off very quicly with the frequency pulse.

**broken link removed**

**broken link removed**

**broken link removed**
(search for 555 on the page; this is probably cloest to what you want except the freq speed is 1HZ)

O.K. I measured amps with a 250 mA meter and it pegged it all the way, but did not blow the fuse in the meter.

After looking into the above links this is my thinking: I need two 555 timers. the first to set the frequency. I believe I can use two resitors, R1 @
7 khm: , R2 @ 400 khm: to set the frequency to 50hz using the first timer. Then use that signal to trigger the second timer through two more resitors to set the duty cycle at 5% or perhaps variable. I haven't figured out those values yet.

Am I on the right track? What effect will potentially higher Amp demands have? My resitor figures are from memory as I wrote them down when I calculated don't have them on me.

The last link in my last post gave you a 1Hz circuit (last link in the post), with 2 diodes to allow the 555 to change the duty cycle. Did you try making that and change the frequency to 50Hz? That sounds like what you are after.

I am affraid the math requried is beyond my knowledge. I am not sure of how to change the frequency. I haven't built anything yet. I am waiting till I can flesh out a good design and then buy/build everything.
How do the diodes let you change the dutycycle? I am begining to feel this is over my head. I am confident I could physically build the circuit. But I am less than confident in my ability to design it. could I simply change some resitor values to get the 50hz? would the rest of the circuit stay the same? I need someone to give me values to use or at least a good formula, as I don't think I am knowledgeable enough to rely on my math.

I never really did anything with a 555, but they are popular. Anyway.

The website in the prior links I sent might explain the diodes. And below is a calculator to get your 50Hz.

Try 1K 1K and 10uF and work it from there.

https://www.hobbyprojects.com/calculators/555_timer_frequency_duty_cycle.html