I’m a complete electronics noob, but this whole Shruti-Shruthi business makes me want to learn a bit of it, so I’m tinkering with my atari punk console, to see if I can hack it somehow. Now, I have a Novation Bass Station which can output CV and Gate from Midi, I was trying to feed the CV into the APC, but it wouldn’t work… The APC uses a 5556 timer (which is two 555 timer ICs combined into one afaik) pin 3 can accept control voltages and there is a pot (500K) controlling the pitch. If I add the voltage of the CV to the voltage somewhere after the pot, I should be able to modify the pitch with the CV, shouldn’t I? Anyway, the result is that the voltage from the CV (roughly between 2,5 and 3,5V) replaces the voltage in the circuit, and does not add to it… and in fact, I don’t hear anything, since the APC runs on 9V and 3V is really to low for it to produce anything…
Now I have one solution that could work: feed the voltage into a led which drives a photoresistor, which replaces the pot… should work, but have to try it out. But still I want to know what I’m doing wrong! I know it’s probably something stupid… but as I said, I’m a noob… so please tell me where I’m being stupid! 
interesting.
modular synth controlling a 555. i like it
interesting.
modular synth controlling a 555. i like it
that's what the 555 CV input is for.. FM 
It works, not the best sounding, but it's a simple circuit.
Next time i'm at my friends place i'll shoot a video of his "the squarewave parade" 555 VCO's that he fracked and then we modified over to Eurorack.
Simple pitch knob, FM input (CV) and FM Amount (simple attenuation of the incoming CV).
you can get some crazy FM sounds modulating one oscillator with the other.. similar to the 556 circuit accept you can use both VCO's independently.
it's good for clocking other modules really.. I'm not a huge fan of the sound of the 555 as a VCO. but it works for simple square and triangle LFO functionality.
Last edited by low-gain (Sep 5, 2010 3:28 pm)
feed the voltage into a led which drives a photoresistor, which replaces the pot… should work
the part you are looking for is a vactrol. they are essentially just what you described... a LED and sensor encased in a black gloop.
might i suggest the wonderful bridechamer for such a part: http://bridechamber.com/bridechamber.co … d_ICs.html
i think that is a cool idea personally, as vactrols give a circuit a certain organic quality, and i personally like them.
however, i've never used vactrols for getting different resistance values from the LDR. only on/off states.... well, on-resistance and off-resistance, really.
the idea is, when the LED inside the gloop is lit, the LDR legs give you the on-resistance (lets say... 100kohms). when the LED inside the gloop is off, the you get off-resistance (could be 0ohms, could be something else... read the datasheet).
however, i really don't know if you could dim the LED and get different resistance values on the LDR.
does anyone know?
edit -- yes, i know LDRs are light-dependent resistors. however, its also the norm (from my exposure) for vactrols to be for on/off switching, at least in modular synths, which does glide slightly when changing states. i just don't know if vactrol LDRs are even made sensitive enough to be used for something like this... that's my question really. i know they glide from on to off.... but, i've never used them to maintain a resistance value between on and off...
alternatively...
you could use a digi-pot if you wanted. i'm sure there are plenty of tutorials for *duino boards that will accept either CV and/or MIDI, and you would need to translate these values into a resistance value in the digi-pot. there is enough support for arduino you may even find this code already available, or at least edited easily.
edit edit - ust to make sure i don't lead you down the wrong path.... resistors aren't what you want for CV control. resistors impede the current flow, which in accordance with ohm's law, drops the voltage. voltage control is what you want. impeding the current flow is not what you want, however. this is part of the reason resistors aren't meant for voltage regulation in a circuit, but people use an IC for this which will not impede the curent like a resistor but will control the voltage.
in other words, its perfectly fine to use vactrols for a switch replacement, and depending on if the LDRs are sensitive enough for analog control, pot replacement.
but, not for CV control.
listen to logan on that one.
First of all thanks for all the replies!
that's what the 555 CV input is for.. FM
really? you can do FM? Didn't know that... I have a batch of 555 timers, I could try building something from scratch, do you know where I can find some info about this? Like schematics or somthing...
Anyway I think I'll try the vactrol trick. They use it in the Voice of Saturn, which is just a derivate from the Atari Punk Console! So it should work... I only have to find the right led-LDR combo... I just ordered some stuff... let's hope for the best.
http://store.curiousinventor.com/all-ki … g-kit.html
uh... dude.. what does FM stand for... Frequency Modulation... >_< all you're doing is modulating the pitch via CV... bam. FM.
Read the forrest mimms book.. it's been a circuit for the longest time.. back before it was call the completely stupid name of "atari punk console"
Last edited by low-gain (Sep 6, 2010 5:19 am)
Well if you put it like that, it's pretty obvious indeed... Well I already succeeded in adding an additional 555 circuit which outputs a squarewave which, connected to pin 3 of the 556 can be either an lfo or at higher values create some FM...
atari punk console is a stupid name, but stepped tone generator is even worse imho... anyway, I'll read the book! Thanks for the tips!
if you want to have some fun.. replace all the resistors in that circuit with pots..
in the one I have there's only one (it's the Getlofi kit). But now I'm about to build a new one... might try the pot thing! there never enough knobs!!!