Motor Timer Circuit

I've built a simple little circuit for controlling the run time of a motor.  It's based on a 555 timer chip in monostable mode — which means when you press the button, it runs the motor for as long as you set with the knob.

It's can currently range from ≈ 1sec to ≈ 12secs.  Modifying this range is as simple as changing a capacitor or resistor.  For example, doubling the size of the capacitor would result in a range of ≈ 2-24secs.

The idea is to use this on a model aircraft instead of rubber band power - which can be a bit of a faff.

I'm not sure about the motor yet - it's just been scored from a CD-ROM drive and the power supply here is a 9V battery - which is quite heavy.  Happily, the circuit will accept voltages from 2-18V so there's plenty of scope for experimentation without having to alter the circuit.

I translated the circuit from a breadboard test to a stripboard layout and used Pages on the Mac to draw a template.  I then printed and stuck the template onto the stripboard which gives a really nice reference as you're adding components.  This diagram is version 2 which ironed out a few layout issues.

If it actually gets strapped to a model plane… you'll see it here.   :)

First Joule Thief circuit

It's amazing thing seeing a 'dead' battery produce useable power!

Alternatively, using this circuit, you can use a regular 1.5V AA cell to light up a white LED which normally only wake up at around 3V.   Very clever!

To learn the how and why of it all, visit Wikipedia

JP helped me do the soldering on this.  He was in charge of the solder (new lead free solder by the way).  I plumped for a big fat ferrite core that I had lying around.  It can be done with teensy tiny cores but I didn't fancy the fiddle - especially with JP and it being my first attempt.

The circuit is built freeform - that is to say without a circuit board.  Heatshrink comes in handy here.  It fired up first time.

Here's a trace of the waveform on the oscilloscope.  If I'm reading it right, it's peaking at around three volts.

The AA cell, under load, is putting in 1.3V at about 40mA

Putting the 'scope into XY mode produces this gorgeous trace.  Fascinating - especially when you realise it's running quite fast... by my calculations, this is running at about 70kHz — 70,000 pulses a second!


For thems that wants to know mores...  I was following the circuit diagram and recipe here.

Enjoy.