Hi
Fiddling around with counters. I assumed there would be an octal version of the 4026 (BCD counter with 7-segment display decoding) and thought it was the 4022. It would seem the 4022 is indeed a counter but it doesn't output patterns of values to drive a 7-segment display like the 4026 - instead each pin just goes HIGH in sequence.
Is there an "octal counter with 7-segment display decoding" or how might I get a 4026 to only count to 8? (or 7 if it begins at 0)
Thanks
Jim
You could reset it when it gets to 8.
I think you will need a logic gate with that drives the reset pin when segments b, e, f, g are on, which only happens when th counter gets to 8.
Draw the numbers out & confirm - 6 kind of drives it because it has all but 1 segment on.
At school we're using the 74160 bcd counter, very easy to use 
Or what's occurred to me since is, could I pulse the clock pin of the 4026 and 4022 at the same time but link the 8th step pin of the 4022 to the reset pin of the 4026 ... or even the carry pin of the 4022?
What am I gonna get? 0-8, 0-7, 1-7, 1-8? Suck it and see I guess!
Yeah, try it. Not gonna break anything.
@Ghiuro,
The 74160 does not provide the decoded output to drive the 7 segment display. You would need a 7446 or 7447 (common anode), 7448 or 7449 (common cathode) to drive the display.
Hmm .. well the 4026 and 4022 are counting from the same clock source (the pulse from a 555 in monostable mode) - the 4026 counts 0-9 and repeats and the 4022 is doing it's 8 step cycle - I connected the 8th step to the unused decimal point on the 7-segment display to check
But
I realised the 8th step on the 4022 probably isn't suitable to pulse the reset pin on the 4026 as in fact the pin remains high for the duration of the 8th step. It's not until the next clock pulse is received that the 8th step goes low again
Connecting the 8th step pin and also the carry pin of the 4022 to the reset pin of the 4026 didn't do anything anyway. In fact I can't seem to get the 4026 to reset at all. If I take a signal from the Vcc rail and touch the reset pin the LED display goes blank but comes back a moment later with the same number. Sometimes if I touch it for longer it comes back with garbage. If I turn the whole circuit on and off it comes back on the same number it was at when turned off.
Help. Rapidly getting out of my depth!
Also, and I assume this is a common problem, how do you start a pin in one state when the circuit first powers up (reset for example) but then set it to the opposite state a moment later and it remain in that state forever - or at least until the juice is flipped again. Is this a job for a capacitor?
Don't know what to tell you about the part not resetting - 200nS wide pulse should do it.
If you want a narrower pulse then AND the 8th bit with the clock line, output will be the width of the clock while Hi.
You are resetting the 4022 at the same time?
2nd part - if you want signal to start out low and then flip high, then yes, a resistor between +5 and a capacitor will let the cap charge up to a high output.
Put an inverter on that line to have it start high and then go low as the cap charges up.
Hi
Thanks.
I was being a noob with regards to the reset - I can indeed reset the 4026 manually now (although it still remembers it's last value when turned on and off but I'm going to assume this is a feature).
But still neither the carry or the 8th step pin of the 4022 will trigger a reset.
I measured the voltages in each instance. The manual reset delivers about 5.6V to the reset pin of the 4026 but the 8th step pin on the 4022 is only about 4.89V when high (I don't have a scope or probe to measure the output of the carry pin). Is it possible that the reset pin on the 4026 expects a minimum value?
If so, and here's another noob question. How do you increase the voltage in a circuit? 'Transistors' popped into my head and I went to read up and realised that a transistor can be used to increase current but not voltage - is that correct? Further Googling suggests it's the job of an op-amp but I've only ever used 741s which require a +/0/- supply - my circuit is only +/0.
Is that the only way to up the 4.89V output of the 4022 above 5V (assuming that's why the signal won't trigger the reset on the 4026)
Cheers
Jim
CrossRoads:
Yeah, try it. Not gonna break anything.@Ghiuro,
The 74160 does not provide the decoded output to drive the 7 segment display. You would need a 7446 or 7447 (common anode), 7448 or 7449 (common cathode) to drive the display.
I know indeed it has a bcd output.. So we use also a transdecoder, '247 or 248