Triple 555 Timer Synthesizer

Thread Starter

LegallowTube

Joined Feb 5, 2018
5
I've started on my first circuit build and I'm having some newbie difficulties. My goal is to use three 555 timers, each controlled by a potentiometer, which will allow the user to create various wave patterns. The only issue I've been having with it is the output. I'd like each rising edge to allow for a quick high signal to the speaker but I think I've been going about it the wrong way. I drew this out if in case it'd be any help understanding what I've been doing:

I'd previously used three npn 2n222 transistors configured in an AND gate style but had no luck. First off, if I completely removed the first two transistors and didn't supply the third with power. The current supplied to the third transistors base was managing to flow through and power the speaker. I'm not certain on what to look out for but I believe npn transistors need to have a very large resistor value at their base to prevent too much current flow? Could that be the issue? Furthermore I'm pitching the AND gate idea since it was more of an experimental idea to see how the speaker would function if it required 3 highs. But any feedback on the trouble I was having would be great.
Lastly I'd like some feedback on how to get a quick pulse from each high output from the 555s. Instead of a continuous high I'd like for the 'whatever' to send out a pulse any time one of the 555s went high/live. Sorry for my lack of terminology and likely confusion here. I'm pretty foreign to electronics but trying my hand at it.
 

Alec_t

Joined Sep 17, 2013
12,735
Welcome to AAC!
Your '1-transistor-unpowered' arrangement was probably allowing current through the transistor base-emitter junction to activate the speaker.
Your present circuit allows the output capacitor to charge but not discharge. Try connecting a ~100Ω resistor in series between the top transistor collector and the +ve rail, connecting the emitter of the bottom transistor to ground (-ve rail), and driving the speaker via its capacitor from the collector of the top transistor.
Incidentally, it's much easier to discuss circuits if you give each component a label, such as R1, C2, Q1 etc.
 

atferrari

Joined Jan 6, 2004
4,576
Try connecting a ~100Ω resistor in series between the top transistor collector and the +ve rail, connecting the emitter of the bottom transistor to ground (-ve rail), and driving the speaker via its capacitor from the collector of the top transistor.
Kind of an unusual analog AND?

Would that work (within reason)? The transistor in the middle seems to have no reliable reference just depending of the instantaneous condition of the other two.
 

AnalogKid

Joined Aug 1, 2013
9,948
The AND will not work.

The way the outputs are configured, the only time the speaker gets a pulse is when all three outputs are high simultaneously. If the intent is for the speaker to play the three tones continuously like a chord, then what you want is an "analog OR" or a summer. If you delete the three transistors, and connect the three base resistors directly to the speaker coupling capacitor, you might not get much volume but you will be able to hear the tones and hear them change as you adjust the 555's. Start with three 100 ohm resistors, one for each 555 output. Once this works we can move on to a transistor driver circuit.

To calculate the correct resistor size, we need to know the power supply voltage and the speaker impedance.

ak
 

Thread Starter

LegallowTube

Joined Feb 5, 2018
5
Thanks for the feedback everyone. I didn't think I'd get much response.

Alec_t - Thanks for the welcome and I'm 100% certain it's the current leaking through the base. I'd removed the +ve line from the top collector and it continued to leak through to the speaker. So I assume once I study up a bit on them this weekend I'll find that the resistors at their base need to be slightly higher. And what's the purpose of the 100 ohm resistor at the collector? I'd assume a voltage divider but I'm not sure since this is all new to me? I'll be sure to try it out though. But as atferrari said, I'm leaning away from the AND gate for the circuit and replacing it with something that'll allow the speaker to respond to each 555's rising edge. That doesn't mean I'm not interested in still making a double gate from transistors though. It's more of an attempt at learning how to rig things with little to no experience- motivating myself to dive a little deeper into learning with each mistake.

AnalogKid - I tried running the outputs of each of the 555s directly to the speaker but fried 6 of the ICs in the process of doing so. From pure guessing, I'm thinking that's a problem with currently leaking through their pin 3s. One IC may go on and the other two may short as a result. I tried diodes, which I'm very inexperienced with, and had no luck. I'm thinking that's my best bet but I may try a slightly different route. Who knows. I may experiment with all suggestions: ANDs, ORs, diodes, and so on just to learn a bit more and see if I get any interesting results.

Colin55 - And thank you for the air horn circuit. While I'll admit I don't fully understand it off of first glance (and I know it's quite basic) but I think I can piece it together and learn a great deal from it once I've got time to go over it this weekend. It looks like they're using an OR configuration and allowing the transistor that's furthest to the right to allow more current to flow through the speaker.

To clear things up a bit I'm going to try and make the end result a quick pulse for every rising edge. A plus would be to be able to modify the width of the resulting pulse. But for now I'm going to take it all one step at a time and not get too far ahead of myself. Anyhow I tried making a picture that may clear things up:

I'm not sure what the ???? would be and I'm sure it's inner workings is quite complex and out of my range for now. I'm assuming gates come in handy with such tasks? I'll keep posted here every time I make a notable improvement!
 

AnalogKid

Joined Aug 1, 2013
9,948
I tried running the outputs of each of the 555s directly to the speaker but fried 6 of the ICs in the process of doing so. From pure guessing, I'm thinking that's a problem with currently leaking through their pin 3s. One IC may go on and the other two may short as a result. I tried diodes, which I'm very inexperienced with, and had no luck. I'm thinking that's my best bet but I may try a slightly different route.
The 555's did not die because of "leaking". They died because the rated output current is 200-350 mA (depending on the exact part number), but an 8 ohm speaker and a 9 V battery combine for 1 amp of output current. I suggest that you look up Ohm's Law.

Diodes will not work because they do not limit the output current. As above, use 100 ohm resistors to sum the three outputs into the coupling capacitor and speaker.

ak
 

Thread Starter

LegallowTube

Joined Feb 5, 2018
5
The 555's did not die because of "leaking". They died because the rated output current is 200-350 mA (depending on the exact part number), but an 8 ohm speaker and a 9 V battery combine for 1 amp of output current. I suggest that you look up Ohm's Law.

Diodes will not work because they do not limit the output current. As above, use 100 ohm resistors to sum the three outputs into the coupling capacitor and speaker.

ak
Just tried what you'd suggested and what do you know? No fried bugs. Seems to be working beautifully... or at least well enough for what a monkey and 3 IC chips is worth. Still going to experiment around with the tripple tripple 5 synth until I'm satisfied enough to go about posting it as an open source project. But I'll be sure to consult with a few experts to make sure I'm not spreading bad practices. As for now, I've got this monstrosity going and like a genius I've plugged it directly into my computer. Nothing fried. Yet.
 
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