Robot Dialogs

 This is a Eurorack Voltage Detector module design. The idea for this comes from combining two previous modules I designed; the Level Display module and the recent Comparator module. This module uses op-amps in the comparator configuration to compare a signal against several reference voltages and display the output of the comparison on an LED.  The voltage levels compared against are approximately: ±9.8V, ±4.9V, ±3.2V, ±0.9V The module has two independent sets of comparators so two different signals can be plugged in at the same time.  The main use for this in my rig is when interfacing modules from various manufacturer's the acceptable input voltages aren't always the same and it's annoying to have to look that up for each module. I usually remember to add the output voltage range in the engraving on my panels so there's no guess work, others don't usually do that. This module will let me quickly see what voltage a signal is at and attenuate/amplify it as needed...

 A Eurorack Comparator module in 6HP. Like the Analog Switch  this module comes from my journey to create a noise gate with modules. Most of my attempts to make a monolithic noise gate have required some form of comparator to determine when the signal goes above (or below) the noise floor, so making it an independent module is likely to be useful. The core of this module is a dual comparator LM393. The input signal is rectified by the op-amps that buffer the input so both inputs on the comparator are operating in the positive range but one of them is the negative half of the input and the other is the positive half. This creates a window from -LEVEL to +LEVEL where the comparator outputs GND and if the input goes above/below  ± LEVEL the output is 10V (or 5V if desired). I made several simulations of the circuit to improve idle noise issues and allow adequate adjustability of the desired level to detect. The latest simulation is here . There's a simple RC filter on the si...

This design comes from a long term project/idea to make a noise gate for Eurorack. I've attempted several designs for a noise gate over the last year but haven't been happy with the result (yet). In the latest attempt I used an analog switch and a comparator and had some success. I decided that those two parts of the noise gate would be fine as individual modules so that's where this came from. It's really a very simple module, there's a buffered input and ouput and a gate input to turn the switch on or off. When it's on the audio or whatever input signal is passed through to the output. The schematic calls out the DG418LDJ (normally open) analog switch. The DG417 should work as well for a normally closed version. The gate circuit is using a few generic NPN transistors to turn whatever the gate input is into a sharp 5V logic signal for the analog switch. There's a simulation here . Of course the design started on the bread board. Then I designed and ordered ...

Update 2023-02-18: There's a new version of this design: v2.1 I don't consider this design done; but, I've gotta start writing it down because I'm carrying too much diagnostic info in my head regarding this thing. One of the early kit's I built was this AI011 VCO . Despite the website saying it uses a Curtis chip (CEM3340) mine came with a clone AS3340A. At the time I didn't know anything about either chip, I just wanted a VCO to build and play with. Overall it is a fine VCO, it sticks to the datasheet's circuit for trimming. I also built four Befaco Even VCO s to use with the polyphonic envelop generator . I was initially on the fence about building my own, but I eventually decided it would be a nice accomplishment to do an entire signal chain from keyboard to output all of my own designs and an oscillator was gonna be necessary. So I bought some AS3340's from Electric Druid and set about making my own design. The AS3340 has a triangle, falling sawtoot...

This is my first filter design for Eurorack. I seem to always use my multi-mode filters (built from kits) in lowpass mode so that's what I've designed for myself. I didn't want to jump into a multimode filter yet, it just complicates things I don't have a good grasp on yet. The module uses 8HP. For this filter I'm using the AS3320 filter chip which I picked up along with various other chips in that series from Electric Druid . When I went to figure out the circuit I ran into the biggest road block which is that the data sheet is nearly useless. It shows a sample circuit for low pass, high pass and other use cases but they are a tangled mess of wires, very poor layout for helping anyone understand the chip. In an age where the data sheet doesn't need to fit in a single page, there's no excuse for providing such bad documentation. Rant over. These chips are clones of CEM3320 and the full data sheet for that is somewhat better. Here's where I found it . In...

This is a Eurorack Mixer module with four inputs in 6HP. It's quite simple and only uses an op-amp and a handful of passive components. There are four inputs and one output. The inputs pass through independent potentiometers for attenuation and the all the inputs are summed and output. Here's what it looked like on the breadboard: There's also a simulation . This type of mixing allows a strong input to effect other inputs (crosstalk) so it's not optimal for an input that needs to be routed to some other place pre mix. Other than that limitation it seems to work just fine. The potentiometers used to attenuate the signal can be audio (logarithmic) or linear depending on how it's getting used.  I'm glad the design works because after panelizing these I got 30 in the first order which is more than enough for me. I haven't found any issues yet with the v1 circuit, but I haven't used them much either. Time will tell. If I make another mixer it will probably ha...