CD4516BE help

Shock_Hazard · Joined: Jul 17, 2015 Posts: 16 Location: Gwynedd

I'm having trouble getting a 4516 counter to work properly, I've ruled out everything I can think of but a defective IC.
What I'm observing is that connecting things to the inputs or outputs changes how the IC behaves, count patterns are fluctuating like there's a floating input, but there isn't. Confused

Even connecting my 'scope changes the output I'm observing! I've got dropped pulses, nothing on Q0, the up/down input seems to de-activate or activate Q0!? Even observing the clock at the input changes the behaviour of the IC!

Circuit info:
The parallel load inputs are all tied to ground, as is the reset.
The "carry in" or "enable" is tied to ground through a 100k resistor, the "up/down" pin has a switch connecting it to +V or Ground through a 100k resistor- to select either up or down counting mode.
The clock has a signal present, applied from another circuit on the same PSU.

I've tried two different ICs and have the same problem which seems to suggest it's my circuit and not the IC, unless a whole batch of them are fucked.
What the hell is happening here!?

P.S. http://www.ti.com/lit/ds/symlink/cd4510b.pdf

synaesthesia · Posted: Thu Aug 06, 2015 2:41 pm Post subject:

Have you checked the power connections at pin 8 and 16? Even without power CMOS chips might appear to be alive, but malfunctioning, if they only get some power through their inputs.

PHOBoS · Posted: Thu Aug 06, 2015 3:05 pm Post subject:

Maybe even measure the voltage on all the input pins to be sure. Also a decoupling cap. directly across the power pins
can sometimes make a difference.

Shock_Hazard · Joined: Jul 17, 2015 Posts: 16 Location: Gwynedd

I've done both of those things already. It's got power and a 100uF cap. Maybe the pull down/pull up resistors are too large in value? But I've used 100k in the past for other CMOS chips and they've been fine.... Confused

Steveg · Joined: Apr 23, 2015 Posts: 184 Location: Perth, Australia

What are you testing it on ... Breadboard? Socket on PCB?
If it is a breadboard, have you tried it in a different location in case one of the contacts are distorted.

Shock_Hazard · Joined: Jul 17, 2015 Posts: 16 Location: Gwynedd

I think I've fixed it Smile

Originally it was socketed in a free-form circuit but I built the circuit on breadboard to test it easier and I think the problem was the clock voltage signal; it was just a little too low!
So I've added a transistor inverter/amplifier to the clock input which pulls the voltage up a little higher and now it works properly.
ALSO I didn't ground my scope lead at the circuit side, this introduced too much interference for the circuit when combined with the inadequate clock voltage. So the voltages around the circuit were fluctuating with some 50Hz mains hum, resulting in the weird missed pulses and changes in behaviour as I probed the different pins.