Point to Point Atari Punk Console One and a Half

What!?? Another Atari Punk Console build?

Wait wait wait people, this one is different, promise.

Waaay back in 1982, Forrest Mims, Radio Shack booklet writer and Young Earth Creationist (roll eyes emoji) published the plans to his Stepped Tone Generator. It used two 555 timer chips (or one 556 dual timer chip). One of the timers was set up to be a free running oscillator, putting out a variable frequency square wave signal. The other timer was used as an astable or "one-shot" timer, accepting a trigger and then staying "on" for a variable amount of time. When the signal from the first timer was connected to the trigger pin of the second timer, the output of the second timer would become a variable pulse width variable rate signal that would jump in frequency based on the width of the pulse of the second timer.

Basically, you've got a fun little noisemaker that can put out interesting reedy tones, the two knobs controlling the primary oscillator and the secondary timer interacting with each other in interesting, quirky ways.

"So how is this different?" you're asking.

This one is built without a circuit board. Also, there's two secondary timers.

Yes. Two secondary timers. Three 555 timer chips like in the picture.

What that means is the tones that the two secondary timers put out are always related to each other because of math! So you can get rock-solid polyphonic harmony out of a super basic circuit. Polyphonic harmony is hard, folks, I chased exponential-response 1 volt per octave voltage-controlled oscillators for a couple years before I got something I was satisfied with.

Extra bonus! You can use the project as a foundation for an Atari Drone Console by building as many secondary timers as your heart desires, and have a huge sweeping monstrous wall of sound!!! Details in the last step.

Right! So put on your harmonious listening hats and get ready to build some magic!

• 3 x NE555 chips. You can use any sort of 555. It's an ancient design, so the original chips are power-hungry and don't always play nicely with other circuitry. There's dozens of different versions out there with modern guts, but they should all respond exactly the same in this circuit.
• 3 x 220R resistors
• 1 x 1K resistor
• 3 x 10uF electrolytic capacitors
• 1 x 10nF capacitor (ceramic disk is fine, multilayer is fine, film is fine, doesn't matter really)
• 1 x 100nF capacitor (ceramic disk or film or multilayer ceramic not important)
• 1 x 47nF capacitor (same as the other ones, really not important)
• 3 x 1M potentiometers
• bits of wire to hook stuff up
• a power supply that can provide 9 to 12V

This build will need a mixer to blend the outputs of the two secondary timers. I'll show two options.

• 3 x 1K resistors
• that's all the first mixer needs. Just three resistors.

Here's the second, fancy mixer

• 1 x TL072 op amp chip
• 1 x 100nF capacitor (ceramic disk is actually best!)
• 2 x 1uF capacitors (electrolytic is fine)
• 3 x 10K resistors
• 1 x 10K potentiometer

• a power supply that can provide positive AND negative voltage, 9V to 12V

The first thing we have to do is get the chips ready. All dual-inline-package chips (like these) have a dimple or notch on one end of the chip. When you position the chip with the notch facing up (north? away from you?) the legs or pins are numbered starting with the top left, going down to the bottom of that side, moving across and then up the other side of the chip. Pins are numbered like that because of something to do with tubes back in the day, and they were round.

So what you'll do to get our three chips ready for combat is bend pins 1 and 8 forward, as though they're ready to charge ahead and impale the enemy with their awesome tusks.

Bend pin 4 up and over the top of the chip.

That's it. Do all the three timer chips just like that.

If we can afford like almost a whole dollar per microchip and decide to get a modern fancy version of the 555, we won't need a big chunky electrolytic capacitor like these. Myself, I'm using the original gangster 555 chips, and they're notorious for injecting pulses of noise into any other circuitry they're connected to. So these capacitors (and the resistors we'll be using later) will basically protect other circuitry from these mean little chips.

Electrolytic capacitors are polarized, meaning we must always hook them up correctly. There will be a stripe on each capacitor (usually light colored) with minus signs in it. That is the "more negative" leg, and in this case, that leg will connect to pin 1 of each 555 chip.

The "more positive" leg of the capacitors will connect to pin 8 of each chip.

Kind of twist the legs of the capacitors around the pins of the chip, with the capacitors tucked neatly under the chips. Leave the capacitor leg twisted around pin 8 pointing up into the sky.

Pin four of the 555 chip is the reset pin. It resets on low, so we want it to not reset so we tie it high!!! You know, to where the positive electricity comes into the circuit.

"Low" and "high" are jargon in this case for a signal that's high voltage (usually at least 2/3rds of the supply voltage, but that figure varies) or low voltage, close to ground. Or less than "high" voltage, I guess. The thing about logic voltage is that it doesn't need to have any current behind it, so we could use a resistor between pin 4 and pin 8. Well, I guess there needs to be some current, but a large value resistor should work just as well as a straight piece of wire like we're using here.

Blah blah blah, make the project look like this. With all three chips.

The primary timer is the oscillator, which is also called an astable multivibrator or free running multivibrator.

Quite a name, huh?

This is the first 555 timer, and it will be different from the other two. When we're done with it, we'll be careful to set it aside so we can remember which one it is.

This hideous, dirty little 10nF capacitor sets the rate at which the oscillator will oscillate, in conjunction with the resistor (variable resistor, potentiometer) we'll connect in the next step.

One leg of the small capacitor connects to pin 1 of the chip. Don't worry, this kind of capacitor isn't polarized, they can go either way.

The other leg connects to pin 2 of the chip. But don't cut off that leg yet! It reaches way around under the 10uF capacitor, to the other side of the chip, and connects to pin 6 of the timer! Super weird, huh? I guess it's not that weird.

Our biggest part!

My construction method uses the largest parts as the physical foundation of the circuitry. So our first little bit of circuitry is getting something to hang on to, cool huh?

First, we're going to connect a 1K resistor to the middle leg of the potentiometer, with the resistor leg stretching over to the "low side" of the potentiometer.

The other leg of the 1K resistor connects to pin 6 of the 555 timer chip. I'm using old thick-legged 1K resistors, which form a pretty sturdy physical structure. If all you've got is thin wobbly resistors, this'll still work okay, just be weaker. It'll get stronger next step!

I hope you haven't gotten a resistor lead poked into your eye or lodged in your skin, but if you do, you can use it to connect the "high side" of the potentiometer to pin 8 of the timer chip.

We're almost done with this section of the project!

To finish it up, take a 220 ohm resistor and connect it to pin 8 of the 555 timer chip. Pin 8 is where these chips get their + power, and these resistors (one will go on each chip) serve to both keep the 555's noise away from other circuitry, but it also somewhat protects the potentiometers from too much current. Atari Punk Consoles are famous for burning up potentiometers. I've done it myself! That smell... good and bad associations, let me tell you.

Now, if you've got a fancy modern 555 chip, you can theoretically skip the 220 ohm resistor for noise reasons, but you might want to use it anyway for smoke-reduction reasons.

There's just one more step! Cut a bit of wire the right length to stretch from the "low side" of the potentiometer to pin 7 of the 555 timer chip. Solder that up and we're good to go!

If you connect +9 to +12V to the long end of the 220 ohm resistor and connect pin 1 to ground, you'll be able to connect a speaker to pin 3 of the 555 and hear a tone! Yay your first synth!*

*I'm sure this isn't your first synth, and it's not a synth, it's just an oscillator LOL :P

Okay, set aside the timer you were just working on. That little guy is basically done.

You'll need two ugly little capacitors, valued at 100nF and 47nF. These values aren't all that important -- anything less than 1uF (1uF is the same as 1,000nF) and more than 10nF will work. And make the two capacitors different values to make the project more harmonically interesting.

Anywhooo, connect one leg of each capacitor to pin 1 of each 555 chip.

Connect the other leg of each capacitor to pins 6 and 7 of the 555 chip. I know in the last picture of this step the capacitor totally looks like it's connected to pin 8 instead of pin 1, but it really is connected to pin 1.

Surprisingly, these two little timer guys are almost done already! They just need resistors.... VARIABLE resistors! Ay-Kay-Ay potentiometers.

Grab yourself two (2) 1M potentiometers. Connect a 220 ohm resistor to each of them just like shown. See, the "low" side of these potentiometers are going to be connected to the + power (through the 220 ohm resistor of course), and this is a convenient way to get that power into the circuit.

Step 10 will blow your mind!

Okay, here we're going to situate pin 8 of the timer right on the middle leg of the potentiometer. The "high" side leg of the potentiometer seems to fit conveniently between pins 6 and 7, the pins that have a resistor lead soldered to the two of them.

Now these timers are done! Just remember to do this step twice.

Well, two wires. Just the power wire and the ground wire. You probably want to mount these potentiometers in the enclosure or panel you're going to use before wiring it up. Seems like a good idea.

But yeah, the + power wire (the orange one) goes to all the 220 ohm resistors. Trim those leads!

The ground wire (the white and orange one) goes to pins 1 of all the 555 timers.

Here's a bit of blue wire connecting the "trigger" pins (pins 2) of the two secondary timers to the "output" pin (pin 3) of the primary timer. Strangely I didn't take a picture of the primary timer, but you can use your imagination, and solder the other end of this wire (blue if you have it, any other color if you don't!) to pin 3 of the primary timer.

Don't hesitate to bend the output and trigger pins all over the place if it suits your build. I didn't bend the pins on mine just because I didn't want to explain what I was doing.

Now, congratulations, you've got a functioning Atari Punk Console x1.5! Except you can't hear it.

Many APC builds just put the output pin of the secondary timer (just the one) to a speaker with the other speaker terminal connected to ground. We have two outputs though, which will be unhappy if you just connect both of them to a speaker or other audio input type connection. They'll fight. Like, charge at each other trying to impale each other with their tusks, remember?

This is the simplest mixer. It's taking the "high" signal from each of the output, running it through a 1K resistor and then there's a 1K resistor to ground, dividing the voltage (+9V or +12V) in half, which is okay because 6V peak-to-peak is an okay value for synthesizer circuitry. Okay maybe 10V peak to peak without any DC bias is better but you know.....

Right, so we're going to connect three 1K resistors together. One of them we will connect to pin 3 of one of the secondary timers. Another of the 1K resistors we will connect to pin 1 (ground) of that same 555 chip. We'll run a jumper wire to pin 3 of the other secondary timer and connect it to the last 1K resistor.

Now we can get an audio signal from where the three resistors are twisted together! It'll work through a speaker but it'll be very quiet. It will be plenty loud into a computer sound card (careful!) or an aux input (careful!!!!)

But! There's a better way!

This mixer will be higher quality, but requires more parts, and perhaps most importantly, requires a bipolar power supply.

If you're already deep into DIY synth stuff, you'll have a bipolar power supply ready to go. Bit if you're a normal person with normal hopes and dreams, you might not even know what a bipolar power supply is!

It's a power supply with a ground wire (zero volts) a + power wire (positive volts) and a - power wire (negative volts). You can make one yourself with a pair of wall-wart DC power supplies, but I'm not going to cover that here. Or you can daisy-chain 9V batteries to get a fantastic (but short-lived) bipolar power supply.

Anyway, pictured here are a 10K potentiometer for volume control, and a TL072 operational amplifier. Looks just like a 555, don't it?

Get the TL072 chip ready by bending pin 4 and pin 8 under the chip.

First, grab a 100nF ceramic disc capacitor from your stash (maybe tangled in the carpet under your desk?) and connect it to pins 4 and 8 of the op amp as shown.

Pins 3 and 5 get bent up and over the top of the op amp. These pins we're messing with will be where the power and ground wires go into this part of the circuit. The two top pins are the non-inverting input pins, which need to be connected to ground (zero volts) for a this kind of active mixer to work. Pin 4 is where the - power comes in to the chip. Pin 8 is where the + power goes into the chip.

Look! It's a used, dirty 10K potentiometer! We'll need to connect the middle leg of the potentiometer to the "high" pin of the potentiometer.

Then we're gonna mess with the op amp a bit more. First, pins 6 and 7 get bent out a little bit like in the picture.

Then we're connecting pins 1 and 2 together. This is just a way to make that half of the op amp not freak out all the time. See, when working with analog electronics, it's a bad idea to leave inputs floating (not connected to anything) and this is a great way to deal with them.

Okay. An inverting mixer like this one is an amazing building block for synthesizers. You can connect any number of signals to the input side, with the mixer providing more or less gain depending on the value of the input resistors. The gain equation is "feedback resistor divided by input resistor" except technically the negative of that number, since it's an inverting amp. But -1 and +1 gains sound exactly the same when dealing with audio.

The way I'm building this mixer the gain will be, at maximum volume set by the potentiometer, -1. So a 6V peak-to-peak signal coming into the input will be a 6V peak-to-peak output.

You can get more output voltage by making the input resistors lower resistance, say, 6.8K with a 10K potentiometer. Then you'll get (math in my head) about 9V peak-to-peak, so it'll be a little bit louder. It's a bad idea to use input resistors less than 1K (stresses out the op amp) so if you need MONSTER GAIN use a larger value potentiometer. But op amp distortion is ugly, avoid it unless you're really interested in, like, crackles and stuff.

Aaaanyway, build it like this and your two 10K input resistors will be electrically connected to the inverting pin of the mixer (pin 6) and the output of the mixer will be pin 7.

I like to use ethernet cable wires for my power cables. For me, orange is always + power, white (with whatever color stripe) is always ground, and green is always - power.

The + power wire goes to pin 8. The - power goes to pin 4. The ground wire goes to pins 3 and 5 on top of the chip.

ONE MORE STEP, you impudent mortals ha ha ha ha ha.

Okay, this project has a single-supply section (+V and ground) and a bipolar-supply section (+V, -V and ground). These two types of circuits don't play nicely unless you use capacitors to remove DC bias.

Also, the relationship between capacitors and the resistance they're connected to affects what frequencies get blocked and passed. We need to pass all the audio frequencies through the capacitors, and just block the DC bias (see, the pulses from the 555 timers go between +V and ground, meaning there's an average voltage somewhere between. The average of an audio signal should always be zero volts, or ground, so that's what the capacitor does.)

In this circuit, a 1uF capacitor and the 10K input resistor allows 16Hz through, which is great. The + side of the electrolytic capacitors go to the output pins of the two secondary timers. The - side connects to the input resistors of the mixer.

And there we have it! Enjoy! I use my APC x1.5 frequently in my modular. It's really quite surprisingly good.

Pin 5 of these 555 timer chips is the "control" pin, which seems to be unused almost all the time when people build circuits with 555 timers. Usually pin 5 is just connected to ground through a small capacitor (10nF seems to be the standard) and ignored.

I'm using the original 555 timers in my build, which are perfectly happy to have pin 5 left floating, sticking out into the air, with ambient voltages and static electricity whizzing around it in a confusing maelstrom of colors and light..........

...anyway, maybe some fancy modern CMOS 555s won't like having their control pin hanging into space. So either connect them to ground through a 10nF capacitors or (this is way more fun) use then as control voltage inputs!!!

You can use a voltage to change the pitch of the three timers in this project! Connect a resistor (10K to 47K, somewhere in there) to pin 5, and connect your control voltage to the other end! With this configuration, a higher voltage means a lower pitch, but we're not after

Here's the other idea. If you build the Fancy Mixer for this project, you can add as many secondary timers as you like. Sixteen. 32. 64. No need to limit yourself to powers-of-two... nine, 27, 81... dang it those are powers of three. Anyway, the Fancy Mixer you built can accept an unlimited number of inputs. Just add more 10K resistors to pin 6 of the TL072, with the 1uF capacitors, of course, and build yourself an Atari Punk WALL.