A short description on how the signal to trigger converter works. The incoming signals are summed up. Every time when the summed signal changes polarity (moving through zero) a trigger is generated. Moving from plus to minus generates a trigger at the negative trigger output, moving from minus to plus generates a trigger at the positive trigger output. Trigger length is about 1.2msec. The gate output stay high as long as the summed input signal stays positive. Trigger and gate voltage is +5V.

Signal to Trigger Converter schematic

The input signals are summed up: Uin1 + Uin2 – Uin3 – Uthreshold. If the sum is above zero volts the output of the comparator IC1A went low. C7 is charged and differentiates the signal. R10 and R13 builds a voltage divider which feeds the comparator IC2C. D4 clamps the negative pulse to ground. This is needed to make sure that the next positive charging pulse starts from zero load in the capacitor. Otherwise the output trigger length will vary with input frequency. R10 and R13 build the unload path for C7. C7, R10 and R13 determines the output trigger length. The comparator IC2C went high when the positive input reaches 7.5V. The output voltage is divided down by R14 and R15. D5 blocks the negative voltage when the comparator switches back to the negative rail. R16 scales the remaining voltage to 5V. IC2D serves as an output buffer. R17 protects the output against shorting to ground. The other path when the summed input signal moves from positive to negative works accordingly.

IC1B scales the output voltage for the gate output to 5V. The output stays at +5V as long as the input comparator stay negative. This means the summed input signal is positive because the comparator inverts the signal.

Summed input signal with positive trigger output

When you have the basics for your synthesizer like VCO, VCF, VCA, ADSR, LFO,… and some controllers and you want more then using your keyboard to steer the synthesizer it is time for some modules to produce trigger and gate signals out of different sources. Here is one of them. A signal to trigger and gate converter. You can feed in a changing signal and every time the signal went through zero a trigger is generated dependent on the direction from where the zero point is crossed. You can add a threshold manually or CV controlled to move the zero point up or down as well.

Signal to Trigger Converter Module

Signal to Trigger Converter schematic

You can feed the signal in through input one ore two. When both inputs are used the signals are added together in IC1A. When the signal crosses zero from positive to negative a trigger of about 1.2msec is generated at output OUT1. When the signal crosses zero from negative to positive a trigger of about 1.2msec is generated at output OUT3. The gate output (OUT2) stays high as long as the signal is in the positive range or above the range which is set by threshold.

Signal to Trigger Converter Sine

The uppermost line (Yellow) shows the input signal. The second line (Blue) shows the trigger when the input signal moves to the positive site. The third line shoes the gate signal which stays positive as long the input signal stays positive. On the fourth line you can see the trigger when the signal is going negative. Those pictures are taken without any threshold.

Signal to Trigger Converter Triangle

Signal to Trigger Converter Ramp Up

When feeding in a symmetrical signal you can generate triggers with a phase of 180deg between the outputs. Using the threshold manually or with CV you can move the phase difference around and create interesting rhythmically changing patterns. There are a lot off more options to discover in combining input signals with the CV and the threshold.

Feeding in random signals is interesting as well. My favorite in the moment is feeding a LFO signal to one of the inputs and using the CV threshold input with a very slow LFO signal. So you can generate some triggers every 5 or 10 minutes. I like this as a reminder of my synths “Hey, I am still here running”.

Signal to Trigger Converter Ramp Down

Signal to Trigger Converter Square

Signal to Trigger Converter PCB

Here is a small weekend PCB project. A quad gate to trigger converter.

Gate to Trigger Converter PCB

A gate to trigger converter can be used in multiple ways. This device can not only convert gate to trigger signals. It converts any fast enough rising positive edge from a signal in a trigger pulse. The trigger pulse length is independent from the input signal. The trigger length is determined by one capacitor and is easily adjusted to your needs.

Gate to Trigger Converter – Module

Those four gate to trigger converter are functionally identical. The input network converts a fast enough rising edge of a positive going signal into a brief positive going pulse. The following op-amp wired as comparator cleans the resultant pulse and forms a square pulse. The second stage cuts of the negative part, shift the output level down to 5V and buffers the output. The trigger pulse lengths is adjusted be changing the value of the input capacitor. The output level can be adjusted with the voltage divider at the output of the first op-amp.

Gate to Trigger Converter – Schematic

Gate to Trigger Converter – Screenshot