Re: looking for a 555 timer circuit

On 29 Jan 2006 21:27:56 -0800, "Wayne" <waynelewis@xxxxxxxxx> wrote:

>I've built the circuit and I'm testing it now. Right now, all three
>outputs are high and stay high (>2V) until I press the reset button, at
>which time they all go low. I haven't waited the 30+ minutes yet after
>resetting to see what would happen. I've double-checked all of my
>connections and made sure I have what is shown in revB plus the changes
>you mentioned earlier. I'm using a 5V DV power supply.

---
Did you make the changes I outlined in my last post:


"In going over the circuit for the last time, (LOL) I found a few
errors:

1. U2-5 should be connected to U1-3, not U1-1

2. C1 should be an 0.18µF polyester cap.

3. R1 should be a standard 2 megohm +/- 5% 1/4W carbon film
resistor."?


In either case, it should be working, but if you didn't make the
changes the timing will be off.

I don't understand whether you're saying that it doesn't work at
all, or whether you're saying that you don't know whether it's
working properly because you haven't waited the half-hour or so to
make sure whether it's working or not.

In any case, to start troubleshooting it, disconnect it from the DC
supply and disconnect all of the loads. Then set R2 to its halfway
point and reconnect the supply. You should see a 5VDC square wave
with a period of 1/2 s (2Hz) on U1-7.

If that works, then the oscillator and the first three stages of the
internal divider chain in the 4060 are working. If it isn't, then
there's a wiring error or a bad chip somewhere. Also, if you press
the PAUSE switch, all of U1's outputs should go low for as long as
the switch is pressed. After it's released, pin 7 should toggle at
2Hz.

Try it and post back with what you find and what kind of test
equipment you have available, and we can devise a troubleshooting
plan.

BTW, if U3 comes up with the outputs all high, (which is entirely
possible and doesn't indicate an error of any kind) that means that
all three pumps will run at the same time for 30 seconds when you
first power up, after which they'll drop into their normal
sequential, mutually-exclusive mode. If that's a problem we can use
the spare gate, a resistor, and a capacitor to build a
power-on-reset which will guarantee that the U3's outputs come up
all low whether you press the PAUSE switch or not. Would you like
to do that?


--
John Fields
Professional Circuit Designer
.

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