DIY Project #02: Passive OR Logic
Jul 17, 2019 16:53:05 GMT
admin, thetechnobear, and 2 more like this
Post by NightMachines on Jul 17, 2019 16:53:05 GMT
!!! WARNING / DISCLAIMER !!!
Everything you do as a result from reading the following posts, you do so at your own risk. While synth DIY is generally safe, you are working with electricity, hot soldering irons, etc. and those things can be dangerous to your music equipment, house and to your health. Please always concentrate when working on your DIY projects and be calm and careful.
DIY Project #02: Passive OR Logic
Alright, you've gotten familiar with the breadboard by now and experimented with - or even built - your first attenuator project. Let's look at another simple and passive circuit which is very useful for your modular synth: OR logic!
OR logic looks at multiple input signals and outputs a HIGH signal whenever at least one of the inputs is HIGH. Why do we need this in our modular? Because it is an easy and cheap way to combine multiple gate or trigger signals into one signal stream. We could of course use a regular mixer module for that, but this is big and expensive compared to what we will build here
Let's start with a circuit that combines three trigger/gate signals into one:
That looks easy! Each trigger/gate input just goes through a diode and then to the output. From the introduction thread you already know that a diode allows an electrical current to flow only in one direction. The symbol of the diode in the above schematic indicates this direction by the way the arrow points. At the tip of the arrow there is a little "wall", which corresponds to the stripe we find on the physical diode component. Current can only flow in the direction of the arrow and it is blocked from the other side by the "wall" or stripe.
So why do we need this? Can't we just combine our triggers and gates directly, for example with a multiple module? Let's look at how electricity will flow through our circuit and see what happens exactly.
Imagine only one trigger input is HIGH, meaning at +5V, and the other inputs are LOW, at 0V. GND is also a constant LOW 0V reference and the output is ... hmm ... what's the output of our module? If it is connected to another module, then this module will want to measure if there is a HIGH or LOW signal coming in, so we actually need to tell our output very specifically if it should be HIGH or LOW.
Take your time with this diagram and let me explain. Input 1 receives a HIGH signal and the electricity travels through the wire, through the diode and now it seeks the path of the least resistance to a LOWer point in the circuit. The diode of the LOW input 2 blocks it, so it can't go there at all. Same with the diode of input 3, no way in! Now it tries GND, which is always "pulling" electricity towards it if you remember. But in line before GND, we have put a 100k resistor which slows our electricity down ... ugh ... that sucks. Isn't there an easier way somewhere? Yes, there is. Right to the output! The module that is connected to our output just needs an input resistance of less than 100k (less than our path to GND), which should usually be the case. So the green arrow shows us the path of least resistance and the way our HIGH signal would travel.
If the other inputs were also HIGH, the same would occur. They'd all just go to the output.
Now imagine if there weren't any diodes, like when simply connecting the trigger signals with a multiple.
Uh oh! Now our HIGH signal could go everywhere unhindered! Where it actually would go depends on the modules we have connected and their circuits (and how they are protected). Now, generally, this will still work and nothing will blow up, but well ... it still might ... we actually don't know and cannot be sure. SO PLEASE DO NOT USE YOUR MULTIPLES AS MIXERS ... damnit!
Just look at the chaos!
Alright, back to our fine OR logic circuit! Remember, we have to tell the output if it's HIGH or LOW. Let us see what happens when all inputs are LOW then.
All LOW inputs would pull the output LOW, but they can't, because of the blocking diodes. So it's time for GND to shine! Yay! The way through the 100K resistor is now the path of least resistance and so the ground pull will keep the output LOW, so that the next module can measure a very well defined and stable LOW signal too.
This configuration of a resistor before GND, to keep a signal LOW, is called a “pull down resistor” circuit, which you will frequently encounter on your DIY travels. There is also a “pull up resistor” circuit, but let’s leave that one for later.
If we wouldn't have that pull down resistor in our circuit by the way, then our output might be undefined and could be influenced easily by radio waves or other disturbances in the force and we don't want that.
Good job reading this far! This circuit is very simple, but it teaches us some important lessons which will be useful for many future DIY projects. Feel free to take a break now and let it all sink in. Or don't ... and get out your breadboard and components!
Breadboard Circuit Test
Bill of materials (BOM):
3x Schottky Diodes (AliExpress)
1x 100k Ohm Resistor (AliEpxress - choose 100K !!!)
Setup
!!! ATTENTION !!!
Switch off the power to your AE Modular system before you start!
I'm sure you can already set this up on the breadboard by yourself, but I'll show you a picture anyway. Don't worry that my diodes look different than the one above. They function the same way but are translucent and have a black stripe at the blocking end.
Please make sure that you connect to the correct GND socket on your AE Modular bus connector or on a module front panel. Here's that picture from the last project again:
!!! ATTENTION !!!
Double-check your patch cables now! You will switch on the power to the system next. This means that your DIY circuit is connected to your modular synth and if you made a mistake, things might break. After powering your system on, immediately check if all things look normal. If you feel something is behaving weirdly (e.g. no LEDs light up, no sound, weird smell) disconnect the power immediately and re-check your cabling.
Now, turn on the power to your AE Modular system and see how your input triggers/gates will be mixed. Remember, as long as one input is HIGH, the output is HIGH too. So when two inputs are HIGH they come out as the same one HIGH signal no matter if one of them turns LOW again.
Congratulations! You just built another synth DIY circuit!
What next?
Of course you do not just have to mix triggers and gates. You can also input other CV or even audio signals. Note though, that all signals are just "mashed" together and clip at 5V, so the output might get distorted and unpredictable quickly. But maybe that's interesting and you actually want that - we're working with a modular synth after all
If you need more than three inputs, simply add more diodes in parallel to the others.
Once you feel comfortable with all of this. You can take the parts off the breadboard, solder them onto a PCB and build your own AE Modular OR logic module. In fact, this is what I will show you next in this thread. So stay tuned
Everything you do as a result from reading the following posts, you do so at your own risk. While synth DIY is generally safe, you are working with electricity, hot soldering irons, etc. and those things can be dangerous to your music equipment, house and to your health. Please always concentrate when working on your DIY projects and be calm and careful.
DIY Project #02: Passive OR Logic
Alright, you've gotten familiar with the breadboard by now and experimented with - or even built - your first attenuator project. Let's look at another simple and passive circuit which is very useful for your modular synth: OR logic!
OR logic looks at multiple input signals and outputs a HIGH signal whenever at least one of the inputs is HIGH. Why do we need this in our modular? Because it is an easy and cheap way to combine multiple gate or trigger signals into one signal stream. We could of course use a regular mixer module for that, but this is big and expensive compared to what we will build here
Let's start with a circuit that combines three trigger/gate signals into one:
That looks easy! Each trigger/gate input just goes through a diode and then to the output. From the introduction thread you already know that a diode allows an electrical current to flow only in one direction. The symbol of the diode in the above schematic indicates this direction by the way the arrow points. At the tip of the arrow there is a little "wall", which corresponds to the stripe we find on the physical diode component. Current can only flow in the direction of the arrow and it is blocked from the other side by the "wall" or stripe.
So why do we need this? Can't we just combine our triggers and gates directly, for example with a multiple module? Let's look at how electricity will flow through our circuit and see what happens exactly.
Imagine only one trigger input is HIGH, meaning at +5V, and the other inputs are LOW, at 0V. GND is also a constant LOW 0V reference and the output is ... hmm ... what's the output of our module? If it is connected to another module, then this module will want to measure if there is a HIGH or LOW signal coming in, so we actually need to tell our output very specifically if it should be HIGH or LOW.
Take your time with this diagram and let me explain. Input 1 receives a HIGH signal and the electricity travels through the wire, through the diode and now it seeks the path of the least resistance to a LOWer point in the circuit. The diode of the LOW input 2 blocks it, so it can't go there at all. Same with the diode of input 3, no way in! Now it tries GND, which is always "pulling" electricity towards it if you remember. But in line before GND, we have put a 100k resistor which slows our electricity down ... ugh ... that sucks. Isn't there an easier way somewhere? Yes, there is. Right to the output! The module that is connected to our output just needs an input resistance of less than 100k (less than our path to GND), which should usually be the case. So the green arrow shows us the path of least resistance and the way our HIGH signal would travel.
If the other inputs were also HIGH, the same would occur. They'd all just go to the output.
Now imagine if there weren't any diodes, like when simply connecting the trigger signals with a multiple.
Uh oh! Now our HIGH signal could go everywhere unhindered! Where it actually would go depends on the modules we have connected and their circuits (and how they are protected). Now, generally, this will still work and nothing will blow up, but well ... it still might ... we actually don't know and cannot be sure. SO PLEASE DO NOT USE YOUR MULTIPLES AS MIXERS ... damnit!
Just look at the chaos!
Alright, back to our fine OR logic circuit! Remember, we have to tell the output if it's HIGH or LOW. Let us see what happens when all inputs are LOW then.
All LOW inputs would pull the output LOW, but they can't, because of the blocking diodes. So it's time for GND to shine! Yay! The way through the 100K resistor is now the path of least resistance and so the ground pull will keep the output LOW, so that the next module can measure a very well defined and stable LOW signal too.
This configuration of a resistor before GND, to keep a signal LOW, is called a “pull down resistor” circuit, which you will frequently encounter on your DIY travels. There is also a “pull up resistor” circuit, but let’s leave that one for later.
If we wouldn't have that pull down resistor in our circuit by the way, then our output might be undefined and could be influenced easily by radio waves or other disturbances in the force and we don't want that.
Good job reading this far! This circuit is very simple, but it teaches us some important lessons which will be useful for many future DIY projects. Feel free to take a break now and let it all sink in. Or don't ... and get out your breadboard and components!
Breadboard Circuit Test
Bill of materials (BOM):
3x Schottky Diodes (AliExpress)
1x 100k Ohm Resistor (AliEpxress - choose 100K !!!)
Setup
!!! ATTENTION !!!
Switch off the power to your AE Modular system before you start!
I'm sure you can already set this up on the breadboard by yourself, but I'll show you a picture anyway. Don't worry that my diodes look different than the one above. They function the same way but are translucent and have a black stripe at the blocking end.
Please make sure that you connect to the correct GND socket on your AE Modular bus connector or on a module front panel. Here's that picture from the last project again:
!!! ATTENTION !!!
Double-check your patch cables now! You will switch on the power to the system next. This means that your DIY circuit is connected to your modular synth and if you made a mistake, things might break. After powering your system on, immediately check if all things look normal. If you feel something is behaving weirdly (e.g. no LEDs light up, no sound, weird smell) disconnect the power immediately and re-check your cabling.
Now, turn on the power to your AE Modular system and see how your input triggers/gates will be mixed. Remember, as long as one input is HIGH, the output is HIGH too. So when two inputs are HIGH they come out as the same one HIGH signal no matter if one of them turns LOW again.
Congratulations! You just built another synth DIY circuit!
What next?
Of course you do not just have to mix triggers and gates. You can also input other CV or even audio signals. Note though, that all signals are just "mashed" together and clip at 5V, so the output might get distorted and unpredictable quickly. But maybe that's interesting and you actually want that - we're working with a modular synth after all
If you need more than three inputs, simply add more diodes in parallel to the others.
Once you feel comfortable with all of this. You can take the parts off the breadboard, solder them onto a PCB and build your own AE Modular OR logic module. In fact, this is what I will show you next in this thread. So stay tuned
