Electronics

A Selection of my Electronic Projects

Bipolar ±15V/1A Power Supply

Simple bipolar ±15V power supply using 7815 and 7915 linear regulators. Since the 7915 I use current limits only at around 1.5A I've added a Polyfuse to cut the output at a constant overload of around 6 seconds to ensure the Transformer (who has a maximum output of around 1A for each of the two secondary sides) doesn't get damaged.

Temperature Monitor Unit

Temperature Monitoring Unit with two adjustable alarms (Warning and Overtemp), that trigger an individual SPDT relay each and also display's it on the front with LEDs. It supports an input supply of up to 40V (Since I want to operate it from 24-27VAC). The thermistor is input filtered using chokes and a common-mode capacitor to suppress HF noise hence making it suitable for longer sensor leads.

It is mounted in a case suitable for standard DIN rails.

High-Power Relay Card

Coils are either driven by a darlington IC (an old L702B I desoldered somewhere) for µC control or all at once by a (darlington-)transistor.

This one turned out pretty well.

Solar System

I developed this system to power one of my servers. As this is a server I obviously want the thing to run at all times but also make usage of solar power whenever available. The solution I came up with is fairly simple, I mix together the load output of the solar charge controller with the output of a 12V power supply through diodes (in my case I used a bridge rectifier). I've lowered the output of the 12V supply to around 11V so that the 12V output of the charge controller has precedence whenever available.

The server is powered using a 12V DC-DC power supply directly from the output of the bridge rectifier. This works surprisingly well and is super efficient. I have this in operation since mid 2016.

Smaller Projects

RF Diode Detector (SMD)

Crude Wideband Amplifier

Prescaler (Telefunken U813BS IC)

Transimpedance Amplifier w/ Bias Voltage Input

Electricity Meter Board

An old electromechanical electricity meter (1P) with a CEE inlet and two standard german socket outlets mounted on a piece of MDF.

Modifications

Chinese REX-C100 Clone SSR Output -> Relay Modification

These cheap Chinese REX-C100 clones are readily available for a few bucks, however one problem you may occur is that they come in two versions, one with a relay and one with an SSR output. Usually you can't really tell which one you are getting, so I got the SSR version but wanted a relay output, fortunately it is really easy to modify. Just desolder the two resistors and replace them with a 12V relay appropriate for the footprint.

Drill Press Light

I wanted some close-up light for my drill press, so I figured lets get a cheap battery powered LED reading light and attach it to it. And that's exactly what I did.

And glued the lamp socket with the batteries onto the wall, because why not.