Single Range Function Generator

Back in 1997, a single-range function generator circuit appeared in Elektor Magazine. The circuit is traditional in as far as it consists of a comparator, an integrator and a triangle/sine wave shaper. However, a special variant of the comparator is employed to be able to cover the traditional frequency range of 20 Hz to 25 kHz in one go.

Originally my build of this project was contained in a Jiffy Case and powered by a 18VAC power brick. This build upgrades the case to a 3D printed instrument case. Also it is now mains powered.

3D printing

The STL files for the case are attached. All printing is done using a 0.2mm layer height. You may need to orientate the parts on the build plate before slicing.

When printing "Single Range Function Generator V1 - Text.stl", switch to a filament of a contrasting color at the start of layer 4.

Print "Single Range Function Generator V1 - Front.stl" with supports. After printing, remove the supports and add the two potentiometers and rotary switch to their respective holes. Do not use washers as the nuts need sit below or flush with the front.

Add double-sided tape to the back of "Single Range Function Generator V1 - Text.stl" and stick on the front of "Single Range Function Generator V1 - Front.stl".

Finally add the BNC connector

Add 4mm diameter by 3mm high M3 brass inserts into the holes on the tabs for the bottom and top clam-shells.

Add 4mm diameter by 4mm high M3 brass inserts into the PCB mounting holes on the top clam-shell.

Preparing the PCB

Previously the old version was powered by a 18VAC power brick. In this build, the unit is mains powered via a 240VAC to +/-24VDC 250mA power module.

First remove or don't install the 1N4004 diodes and the 2-Pin JST socket from the PCB.

3D print "Power Holder.stl" and super glue it to the PCB as shown below.

Wire up the -24V, 0V and 24V connections as shown below. (Note the 0V connection on the power module spans the two middle connections)

Electronics

I designed a PCB to hold the components. External connections to the PCB use KF2510 connectors to keep everything tidy.

The Eagle files are attached if you wish to get the board commercially made or you can do as I did and make it yourself. I used the Toner method to make mine.

Remember to leave off D14, D15 and J6 when assembling the PCB.

One of the changes to the original design was to replace the 4-pole 3-way switch that sets the waveform to a 3-pole 4-way switch. The extra position is used to switch off the power. This is achieved by using the spare two poles to switch on the +24V rail and -24V rail from the power supply to the PCB when a waveform is selected.

Wire up the potentiometers, rotary switch and BNC connector.

Screw in the PCB to the case bottom using four 4mm M3 screws.

The top clam-shell is held in place using four 6mm M3 black hex screws.

Conclusion

The 3D printed case is certainly an improvement over the Jiffy case.

Discreet electronics without microprocessors is still fun. It's a pity in some-ways that it is a dying art but if you are interested in looking at old electronic magazines, the best source that I have found is https://worldradiohistory.com/