Hey guys... I would like to try to make this but the schematic is such a mess! All of the connections that should goto a DIP aren't! I'm mostly wondering what R1 and R3 are all about? Please help!
But note the dotted box bottom left, unused 40106 inputs must be grounded. It also doesn't use the 741 offset-null pins 1 & 5, common practice on simple circuits, and a 741 pin 8 is not connected anyway. R1 & R3 "from second circuit if needed". If you don't add the second (duplicated) circuit, you don't need them. They're mixer resistors, think of them as R2b and R7b, where the 2 circuits' signals join up.
cpemma what needs to be grounded if not used? I think I understand what they mean now, basically you'd just repeat that entire thing the exact same way as it is shown, and then it will ouput into that resistor and to the final output. So I don't need it you're right. Does this look right? Minus the power supply circuit? http://www.flickr.com/photo_zoom.gne?id=57328750&size=o
OK, if that wasn't clear, here it is very simplified. The cd40106 is a schmitt trigger with 6 units on the chip. The basic schematic only calls for three. A schmitt trigger left with its input 'floating' can behave unpredictably. So to prevent it from acting odd, you tie the input of the ones you are not using to ground (Vcc would work too, but then they are consuming current, and that wastes battery life). As for the op-amp, the offsetnull pins are there to correct for certain problems with op-amps that makes them behave in some way other than the ideal case. But since the circuit isn't high precision, you can ignore the pins. This is because of the way those pins work, they are sensitive to current, and no connection means no current. The circuit looks like 'an oscillator gated by an oscilator, which is controlled by another ocillator'. Each scmitt trigger froms an oscillator. The two on the left side are pretty easy to see once you know what you are looking at. The pots on 'wacky' and 'zany' controll the rated the caps charge and discharge at, so they set the frequency. 'Weird' is a little trickier. Take out the transistor and it looks like the other two oscillators. But with that cap, things change a bit. The zany circuit will drive the transistor between saturation and cutoff so it acts as a switch. What it is controlling is the voltage on the cap c5. The effect is that the weird frequency is modulated by zany. The modulation is FM, not AM because zany controls the rate of charge and discharge of the cap. So this will be dependant on the frequency of zany. Wacky also does somthing to control the frequency of weird. Because of the diode, it can't drive the input of weird at all. But, when wacky's output goes low, it provides a discharge path for cap c5. While wacky is low, weird cannot oscillate, so it's gating weird. The effect is another modulation, but this time it's AM (more like OOK, but that's a form of AM with 100% modulation). Basically, it's a 3 operation synth. The filter network took a bit longer to work out. The cutoff frequency of what is fet to the invrting input is pretty much fixed at about 32Hz if I calculated the frequency responce right (and the 741 is behaving like an ideal op-amp). The 'bypass' to the inverting input shifts the frequency responce graph of the filter, and I calculated it to be adjutable from ~30Hz to ~300KHz. I cold have easilly made a mistake, I often do However, assuming that the inverting input=noninverting input=virtal earth (as set by R20 and R21) then I sould have calculated the resistances parallel to each cap properly and, subsequently, the poles caused by each cap. The total frequency responce is based on the difference in signal fed to each input of the op-amp. It looks like a good starting point for more syth effects. Adding notch filters, wave shapers, and more operations to the system could keep the person playing with the synth busy for weeks
http://meme.no/locomofon/usg1.php Samples of the synth... I believe I understand what those extra resistors are for, and how to expand the synth... I'm guessing C4, C5, and C6 need to be different to create new sounds? Maybe not. Am I correct?
Oscillator frequency for the single gate sections is 1/(CxR) so the range of U1-B with the 0.02uF cap is from about 50Hz (R=1004.7k) to 10.6kHz (R=4.7k), covering most of the audio range. With U1-C's 1uF it's 50x lower, 1Hz to 212Hz, used to modulate the sound. Log (audio taper) pots look a good idea for the 1M sizes.
I am in the middle of this circuit. My son is fascinated with weird sounds and blinking lights (aren't we all ). What I want to do is add at least 1 4017 as a light chaser to represent the clock pulses from the Schmitt trigger. Am I correct in thinking that I can connect pin 14 (Clock) of the 4017 and pin 2 of the Schmitt trigger to get the desired results? Also, will the frequency be too high to see the LED's "chase" and would a small cap make a difference? I understand the basics of Schmitt trigger, I think, but what is the difference with an inverting trigger. I don’t understand the single input. I was going to use linear not audio pots. Why would the audio pots be better?
Think of it as having common grounds, in & out, connected to the chip ground. Or maybe this explanation will help. From the f = 1/RC formula, with a linear pot on maximum in first above example you get 50Hz, turned half-way gives 100Hz, on minimum for 10.6kHz. Seemed to need a less linear approach to spread the scale out a bit better.
Thanks for the answers. Helpful as always. Any chance of getting help with the first question about the decade counter?
It's a bit guessy, but fastest visible might be if the 4017 cycles through all 10 leds in 0.2sec, a 50Hz clock. Sticking with the 4.7k minimum resistor, that would be a 4.7uF cap (actually gives 45Hz). Then adding a 100k pot would give a minimum frequency of 2Hz, each led lit for half-a-second. A bigger pot (say 470k) will make it even slower, a smaller cap speed up the fast end. But there's no problem using a logic gate oscillator for the 4017 clock; I guess the best reason for a 555 being more common is the smaller package, only 8 pins to deal with. For increased accuracy and stability, using a second gate as a buffer, as here, will help.
If you wanted to tie the LEDs to the actual ocilliators, you would need to divide down the frequency so that the highest frequency switches any single LED at a frequency no more than about 15Hz. At aroung 18Hz, they should appear to flicker, and much higer and they look like they are constantly on. But you could build another ocillator as cpemma suggests and use a ganged pot (2 pots controlled by 1 knob) so the change in frequency has a visable correlation with the LEDs. If you did want to try the divider route, start with the fastest flash rate per LED of 15, multiply it by 10 for 10 outputs for 150Hz max input speed. Say the highest frequency is 10KHz to make things easy and divide that by 150. Thats a divider of about 67 times. If you cascaded the 4017s, each divides by 10 so you'd need to cascade 7 of them. Then you have the problem of the very low frequencies. The LEDs wouldn't appear to move at all.
So I'm going to just try this thing out, and see what I get. I'm not to concerned with the hows and whys quite yet. I'm confused though, why would the log pots be better?
It has to deal with the way you hear frequency. If you take a sound editor and generate a lfile that last for so many seconds, say 10 and make it linearly scale from 20Hz to 20KHz and play it back, the lower tones seem to sail by quickly but the higher frequencies seem to drag out. This is because much of the human ear's sensitivity is focused around 400Hz to about 4KHz which is where most of the frequencies fo intelegable speech reside. You can differentiate between say 1KHz and 1.2KHz better than 10K and 10.2KHz. A log pot will change it's resistance very slowly at one end, but much faster at the other. This makes it act more sensitive at that lower end than the higher end. the graph on this page should help. Lots more info here.
