MGL Avionics User Forum

Hello all,
As a long-time MGL user I recently purchased a new project, a DAR Solo 120 with a Polini 2-stroke THOR 250DS engine. I only have most experience with Rotax 912 and resources are rather limited for the Polini. Can please somebody show me the best way to connect an MGL instrument (e.g. ASV-1, Xtreme+RDAC) with the Polini so I can get the RPM readings? Right now there is a small RPM instrument which gets its signal from a coil around the spark plug cable (similar TinyTach). I think this is an option which does not work with the MGL intruments.
It seems there is a way of getting the signal from the "kill switch", but I am not sure which conection to use. I have attached the electrical diagram for clarification, many thanks.

https://drive.google.com/file/d/1e00omK ... sp=sharing

Michael from Germany

It would appear you have several possibilities.
What we are looking for is a A/C signal that is as clean as possible related to RPM. It should ideally have an amplitude of at least 5Vpp. It may be overlaid by DC - we are only interested in the A/C component.
The best way to find out what you can use here is to use an oscilloscope and probe the various points. A portable scope is just what you need.

Failing this, I'd get a small 1:1 or 1:2 audio transformer (the typical 600 ohm types or something close, not very critical). Connect one side to the A/C output that goes to the regulator (i.e. the A/C voltage to the regulator/rectifier in your diagram) and the other side (lets call it the secondary side), one end to ground and the other is your RPM signal for the instrument. You can load this with a resistor (say anything around 0.5 to 1 KOhm) to get rid of any small spikes. This arrangement tends to work quite well with any engine that provides a generator like A/C winding for a regulator rectifier.

You may also be able to use the A/C signal at the input to the regulator directly - the quality will depend a bit on what the regulator does.