Re: 4017 Counter skips under load
- From: Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 02 Jul 2007 14:28:04 -0700
jcargile2001@xxxxxxxxx wrote:
I have a fairly simple circuit that consists of a 4017 decade counter
and nine relay/LED combinations. The relays are very small and the
circuit operates just fine with no load, or when I connect an LED to
the relay output. But when I try to operate the circuit under load
(it is being used to fire nichrome ignitors), then the counter simply
skips the loaded relay and moves right to the next output. So if I
send the counter a series of 5 clock pulses, and put a load on the
relay attached to output 3, then the count goes 1,2,4,5,6. The final
count ends up being one off, so it's almost like the output in
question doesn't exist. What I don't understand is why this is
happening, since the relay is what bears the load, not the 4017.
Shouldn't the output requirement on the counter be the same regardless
of what the relay is switching?
Looks like power supply spikes, sub-optimal decoupling or a substrate diode gets hit. Time to crack out the storage scope, I'd say. Hang it onto VCC of the 4017, then to the pins.
--
Regards, Joerg
http://www.analogconsultants.com
.
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