Diode voltage drop at CMOS input? Help needed :)

[HexInverter]

Well, first off - hello! First poster here. I've been lurking these forums for a while now, but haven't bothered to register until now

I love CMOS based noise generators! I have made tons of whacky 4093 based oscillators, played with 4040/555's/4046/etc, and built a couple of 4017 sequencers successfully. I have a bunch more IC's on the way that I can't wait to mess with!

Anyways, I've ran into a bit of a block that I can't seem to figure out. I'm hoping it's something super easy that I haven't learned yet! Anyways...

I got this great idea from the book "Handmade Electronic Music" to make a modulated clock generator, and want to use a 4093 as the clock input on a 4017. The book suggests chaining the 4093's 4 oscillators and using that as the clock - this works great, but I want to be able to switch each oscillator on and off at will and not interrupt the others (by making the inputs high/low on each oscillator with a switch). So, I mixed the 4 outputs down with diodes and put that through the 4017 - nothing! Connecting a speaker gives me sound from the diode mixed 4093 clock, so I know it's working. The first step of the sequence stays on but the clock does not advance!

Is this because of the voltage drop from the diode/s causing it not to actually clock the 4017? I added a capacitor at the input thinking it might help...no go.

Also, I tried mixing with 1ohm resistors instead thinking it might still pick up on the signal. Still nothing!

Sorry if this is a stupid question...I have probably been going at this too long without a break Prolonged exposure to all the crazy noises has probably done some brain damage

Also, if it matters any, I AM using proper bypass caps on each chip, and a larger electrolytic power supply bypass - the circuit works fine without the diodes/resistor mixing!

Thanks for any help

[DGTom]

Hi! First off... no amount of crazy noises can do brain damage
quite the oppisite I think

I've found unbuffered 4017 clock inputs to be a little fussy, in my lunetta 4017 module I had to put a resistor inline with the input to get it to work at all, so the input is 10K -> Diode -> 100K to ground -> 4017 clock pin... dunno why, but, it worked.

However... I'm going to guess the problem here is with getting a decent edge, I'd bet with diodes, or 1ohm resistors, jamming 4 asynchronous clocks together the signal never gets to 0, so there is never a strong enough positive going edge for the 4017 to recognize - just a guess.

Try fewer clocks into the diodes.

The other way to do it, starting from the Collins idea, set up the chained 4093s, but, use SPDT switches on the pin that is turning each clock on / off.

One side of the switch goes to the preceding clock, the other goes to +V. That way you can toggle each clock between on & modulated.

Feed the 4017 the output of the 4th 4093 clock - the one furthest down the chain - this way differant switch combos will produce differant modulated clocks or 4 independant clocks etc.

Or, I'd look at processing / conditioning the output of the diodes;

http://musicfromouterspace.com/analogsynth/mmlogic.html

start with the MML 40106 OR gate, maybe a one shot... just abuse the signal till it does what you want

[HexInverter]

[bingmachine]

Might be obvious, but do you have a resistor to ground also (after the diode)? If the signal is to pass the diode there has to be a current, and that current has to go somewhere. It won't go into the 4017, unless the voltage passes e.g. Vcc + 0.7V, and I don't think that is what you want. Have a look at MFOS like DGTom suggested, and you'll get the idea.
/Erik

[HexInverter]

[DGTom]

always something simple! Stupid me, I assumed there was a 100K to ground from the start - you know what they say about assumptions!!

[Rykhaard]

Another great way to get a bizarre clock stream into the 4017, is to plug the outputs of the 4093s, into 4070 XOR inputs.

4093 out #1 to 4070 Gate 1 input 1
4093 out #2 to 4070 Gate 1 input 2
4093 out #3 to 4070 Gate 2 input 1
4093 out #4 to 4070 Gate 2 input 2
4070 out #1 to 4080 Gate 3 input 1
4070 out #2 to 4080 Gate 3 input 2
4070 out #3 past the 100k to Ground into the 4070 Clock in.

BTW - great to finally see another Canadian noise maker! I'er beiginning to think I were by myself in this country.

[HexInverter]

[Rykhaard]

[HexInverter]