This is almost as old as the hills – a 555 timer based alternate LED flasher, easily built for under 50p a go! Mock alarm, alien eyes, level crossing ……. pcb is just 25mm square. LEDs can be spaced as you wish either wide as shown above or anything in between, just choose as you build. There are several Android based 555 calculators to provide a insight into customizing the flash rate.

Another old favorite, this a a 6 LED random flasher and can also be built for under £1. As it comprises 6 identical circuits it is almost always going to do something, even with poor soldering. A useful exercise in fault-finding based on symptoms, a flow-chart would be an excellent idea – there are only really 3 main faults, on all the time, flashing too fast to see, or off. Looks good on top of a Christmas tree, or as an attention getter. Super-simple to change the flash rate – a capacitor or resistor change is all that is required. Cheap ping-pong balls (144 for £10 on ebay) make great diffusers especially if you carefully sand away the rounded lens on the LEDs – take CARE!

This next one delivers a LOT of functionality for such a simple circuit.

There is NO on/off switch required – when its not powering the LED(s) or buzzer it draws less that 1 millionth of an amp 🙂

It reacts to the touch of a finger between two pads or wires (e.g. steady hand game where the user becomes the actual wire, so ‘cordless’ or ‘wireless’). The time delay can be increased up to about 2 minutes by changing a resistors and/or a capacitor. The output provision is for 1 LED plus a resistor, 2 LEDs or a transistorized buzzer. Choose depending on your application. The circuit lends itself to a number of pupil friendly applications, not last the endlessly popular steady hand game, but also bedside night light, engraved acrylic clock (touch the pads to light up the dial) and such like. Ideal power source is a PP3 alkaline or for extensive LED usage on longer time delays, 4 or 6 AA cells.

Last but by no means least and a bit of an adventure this one, its basically a self-clocking binary counter with an activity light (so you know something is happening) ‘Time up’ light and a ‘time up’ annoying bleep. As built it offeres a time delay of 1 minute up to 30 minutes. About all the user needs to choose is the colour of the two indicator LEDs. Why bother with this when an electronically simpler solution that delivers the same sort of thing could be built with a PICAXE chip? Well, no programmiong knowledge or facility needed, cheap in comparision, easier to packsage with the reccomended PP3 9 volt battery. Can be extended to one or even two hours. For advanced understanding/extension material, there are lots of useful principles in this circuit that can be used to teach electronics, not least binary counting (additional LEDs could be added to the counter outputs for visual interest/count progress), enabled/disabled schmitt trigger oscillators, inverting a signal and driving a piezo in antiphase to make more noise. Annoying bleep frequency and speed easy to change (just a resistor). It does need careful supervision when inattentive pupils try and build it – in particular resistors wrongly placed or diodes the wrong way round, but nothing some decent QA during the build process should not cure.