Hi everyone! I’m on a project where I try to get an old telephone switch (in German “Hebdrehwähler HDW 27”) to work again. I took a SparkFun MicroView, connected an old (modified) telephone (just the wires from the dialer & cradle), two electromagnetic relays, a power adapter with 48V/60W and a stepdown converter for 5V, put them all together on a 3D printed board… and it works like a charm! The display tells me to pick up the speaker, then it wants me to dial a 2-digit number. While I’m dialing, the MicroView live-reads out the dialer and works the magnets on the HDW 27. After that I have to hang up and the HDW will be triggered a few times to get reset for the next call…
The only problem: at the second or third use of the magnets (dialing the 2nd number or hang up-reset) the MicroView screen goes black, but everything else works perfectly, only “blind”. When I pull the plug and start over, the display comes back like nothing happened. I tested three different MicroViews, all with the identical behaviour. For cross testing I removed the power from the step down converter and connected the MicroView directly with a seperate power adapter (5V), which fixes the problem. Since I have no equipment to thoroughly measure the current from the converter, I wanted to ask: what conclusion can you draw from that behavour (screen goes blank, but works)? Is it a spike in current or an “outage”? The integrated Arduino keeps working without interruption or reset…
Which converter is being used? Share a photo of the soldering/wiring
From the main power adapter two lines go to the relay switches to power the two magnets of the HDW 27 (bottom left), and one line to the step down converter from which the MicroView is powered. The first dialing works fine, the second sometimes blackens the screen, the 3rd dialing (HDW 27 doing reset movement) always does. Now I wanted to know, if anybody got experiences with the MicroView regarding the screen shutting sown (but the Arduino still works without problems)… could it be a spike in the voltag (apply resistor) or a drop (apply capacitor)?
I just rewatched the first video that I took after completing the setup and noticed, that the screen stayed on all the time. So the problem did somehow pop up afterwards, and it affect all three MicroViews that I have (which rules out trouble with the MicroView itself)…
Maybe try powering the microview with. 3.3-16v battery source separately…a standard 1s lipo would be great. I’m thinking the dc-dc converter might be causing/experiencing big fluctuations
That’s what I suspect too, but fluctuating in which direction (resistor or capacitor)? I’d rather try to “minimal-fix” the current build instead of adding a separate power adapter to the 230V input… 
You can just grab a set of dupont wires and skip the breadboard for testing