Monday 10 August 2015

The FG-100 DDS Function Generator

I needed a stable sine wave oscillator that I could use for a couple of projects.

After a quick search on the net I found I could buy a multi-function generator via Amazon for only £27 post free.

A couple of weeks later the FG-100 arrived, with absolutely no documentation. Fortunately it is very easy to drive.

What you get

All you get is the generator and a USB to power-plug cable.

This generator can be powered from a computer USB port or a typical 5Volt USB charger/power unit.

How to use

The "MODE" switch allows selection of waveform type: sine, square, triangle, sawtooth, or reverse sawtooth.

To set the required frequency you have to:-
  • stop the generator using the Run/Stop button
  • press the Cursor button to highlight the digit that you want to change on the lcd display
  • use + or - to increment/decrement the selected digit
  • repeat for each digit
  • press Run/Stop to start the generator

Other controls allow you to offset the waveform via a DC offset feature.

For example, if you want the signal to be centred about 0Volts, just turn off the DC offset. If you want the signal to swing from 0Volts to some positive voltage (or negative value), turn on DC offset and adjust the level.

The Amp control sets the level which is output via a BNC socket. I recommend you buy a proper BNC to crocodile clips screened lead, rather than poke bits of wire into the socket, as I have been doing over the last few days.

I've no idea what the Filter control does! It must filter the output somehow, but I don't see any noticeable change to the signal when viewed on my cheap oscilloscope module.

Output level/frequency

The output level seems very stable while changing signal frequency.

I set the level to give 4Volts peak-to-peak at 1000Hz, and over the range 100Hz to 100000Hz the level didn't appear to change by more than +/- 100mV (and this variation may have been due to my cheap scope).


At just £27 I think this signal generator is great value for money (

I don't know when I'll be using sawtooth or triangle waveforms...

this is a reversed sawtooth

...but sine and square wave signals will be useful for sonic and ultrasonic projects.

Frequency selection appears to be accurate and stable. The only downside is that you cannot just turn a dial and sweep through a range of frequencies. But this is not a huge issue.

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