As per title, what’s the cheapest and easiest way to generate and then measure a 0-12v square wave 124 Hz signal?

It’s to calibrate vehicle tachometers, so the frequency resolution/accuracy is fairly important. Obviously if the tester is accurate, and the generator is adjustable, that would do nicely.

In replying, please bear in mind I know sweet FA about electronics.

Of cheapest and easiest you proably need to pick one. The cheapest would be to make something, probably using a 555 timer (the circuit is called an astable multivibrator… ooer). There’s loads of circuits on the net or you can buy a kit from somewhere like maplin. That’ll get you change from a tenner. For a bit more money and less fiddling buy a signal generator eg signal generator, this does much more than you need so there is probably something cheaper.

To measure you just need a multimeter that measures frequency, probably £20 or so from maplin or ebay for a budget one, £60-£100 for a posh one… or get one of these if there is any benefit in seeing the waveform cute oscilloscope

Thanks nickjb, was already looking at Maplins multi-meters and signal generator kits, but that mini-Oscilloscope sure looks like fun!

Build yourself an astable multivibrator (ooh err).

Cheap as chips and dead easy: http://en.wikipedia.org/wiki/Multivibrator

p.s. you can use frequency analysis software on a computer to check the result. Much cheaper than a real oscilloscope.

This is meant for audio (and free), but with a resistor to reduce your input voltage from 12V to 2 or 3V, and a suitable cable it will work fine: http://www.trueaudio.com/rta_faq1.htm

Cheers glenh, going to have a good read of that, looks promising.

Thanks for taking me back to school electronics lessons, 555 timers, 747 amplifiers and the way Miss Spivey said ‘ticker tape timer’ with her northern accent. Happy days 🙂

Slightly tangential here, but why do you need a square wave? It has infinite bandwidth and can therefore never be generated perfectly, a good square wave will require lots of bandwidth (compared to the period of the wave).

Do you just need an edge?

Regardless, I’d be looking in RS, Maplin etc. for a cheap signal generator and oscilloscope. Unless you have ages to spend getting your hands dirty there is most likely no point in trying to build one for yourself.

12V peak to peak is a hell of a lot of power though (at least into a standard 50 Ohm load which is what most test equipment is designed for). You may well need an amplifier to get that amount of power, which would probably need to be linear-ish to get you a decent square wave. Do you know what kind of a load you are driving?

Also, to measure the response of your system, you will need either an equivalent time scope (cheapish), a real-time scope (more expensive) or some kind of spectrum analyser (in the middle). Difficult to know what to recommend without knowing the details of what you want to measure.

One problem you will have is that the lowest specced test equipment at the minute will have MHz of bandwidth. Getting down to the 100Hz range might be a big fiddle.

fwiw if you’re calibrating something a 555 just isn’t going to cut it. If you are calibrating lots then just buy a function generator of some sort from Amazon. This will go up to 10V – would that be enough
http://www.amazon.co.uk/GW-SFG-2004-Function-Generator-Frequency/dp/B003A5ZA6G/ref=sr_1_12?ie=UTF8&qid=1348156910&sr=8-12

Edit – even cheaper, still 10V
http://www.amazon.co.uk/Function-Generator-Dds/dp/9792263985/ref=pd_sim_sbs_ce_1