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.   :)

GRZR Robotic Lawnmower is Mobile

For the first time, our robotic lawnmower project has mobility and a modicum of intelligence. Two bump sensors dictate which way the robot should turn on impact with an obstacle. It's still early days.



The robot is powered by 4 AA cells via a boost regulator that gives us a constant 5V.  An Arduino does the thinking and drives 2 continuous rotation servos.

We also did a test today on the blades and motor.  Bottom line - it works well when there's not much grass to cut but the tiny motor soon gets bogged down and the blades lose speed.  We're going to need a MUCH more powerful motor and that will mean we need to re-think the power source for the whole robot.

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.

Guernsey Racing Limpets™

You saw it here first folks!



If you want to learn to how to build a Racing Limpet contact Gen at www.thegallery.gg and sign up for my Limpet Racing Masterclass (should be on Sun 31st July).  I can't wait!

ArtBot making

I'm soon to be teaching a class of children how to make ArtBots — a type of vibrating robot that has felt-tip pens for feet.  Fun fun fun!

Alternatively, the 'bot can be decorated and dressed up as a weird and wonderful new creature the world has never before seen then left to explore it's new environment.  Sort of a robot pet.

To be a part of the fun contact Genevieve at www.thegallery.gg

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Reforming plastic - experiment one

I've had an idea for a while to reshape plastic with heat. Specifically 200 liter barrels!

The first experiment has been to pop a drinks bottle in the oven. ;)

I put a dash of water in it and spun up the oven to maybe 150C. It made a little steam pressure as the temperture rose.  Fairly soon the bottom of the bottle made a rather nice balloon! :)

I pulled it out just in time before it burst. It's thin but pretty strong.

The experiment has confirmed a few thoughts in my mind;

1. it's doable
2. the vessel needs containment otherwise the expansion runs away at the weakest point.

Next step... not sure yet. ;)

All together now...

I've been playing with some code and simple hardware that allows the Arduino to pretend to be a USB keyboard...


And, now, when you hook up all the recent bits... shiftIN, shiftOUT and Virtual USB Keyboard...


BIG thanks to Jonathan Oxer and Philip J. Lindsay for sharing their code and methods!

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Arduino and loads of LEDs

Needing to hook up lots of LEDs to an Arduino?  The obvious choice is to simply hook the LEDs to the digital output pins and away you go.  However, this will only give you 14 LEDs.

OR, you can hook one of these fellas.  Catchily named "75HC595" - but known as a Shift Register.  From just three pins on the Arduino you can drive 8 LEDs!  and the fun doesn't stop there... hooking up another one of these puppies to (essentially) the same pins gives you another 8 LEDs :- a total of 16 LEDs off just three pins on the Arduino!!  ...I don't know what the limit is but I've seen somebody driving 24 LEDs with three of these chained together. Very cool.

So, here's what I've done so far...

First up - one '595



Next - two '595s — I just ran out of red LEDs!



Lastly - I added a potentiometer to control which LED is lit.





It's a ball and it's pretty darn simple!


Next challenge - experiment with a similar chip... "74HC166" ...which allows eight buttons or switches to be connected to three Arduino pins - and can be chained together also!   ;)


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DC Motor Driven by Arduino

At last, I've mustered up the courage to hook up a DC motor to the Arduino!

The reason that it's a big deal is that you can't connect a DC motor directly to the output pins on the Arduino - it'll draw too much current and fry the Arduino chip.  This method uses a transistor to switch the large amount of motor current with a small amount of 'control' current.  As an added level of safety for the Arduino, I've also use an Opto-Isolator which a means of completely separating the two circuits - control and output.  Unless I do something silly (!), the Arduino should be safe.  (I already fried one transistor in testing because I'd forgotten to put a diode across the back end of the motor!)

BIG respect and thanks to Mike Cook for his excellent article on hooking up motors.

My circuit diagram is a hacked together version of a couple of his diagrams.

(used with permission - thanks Mike)

The immediate application is for driving the blades on our learning project GRZR - the robot mower!

Lemon and Potato Battery!

Today we made a battery out of Lemons and Potatoes!

This came about from the question "What is electricity?"  I had suggested that electricity is not a source of power... ie. you can't go dig up some electricity out of the ground!

John's smart reply was "of course not, it grows on trees!"   (I like his sense of humour)

We all laughed because that's nonsense.   Right?

So, this week, we made electricity from Lemons and Potatoes.  (thanks Dad)

Harvey and John wired the four together with copper and zinc (galvanised) nails inserted into the ends of each fruit/veg.  The lemons made 0.9V whereas the potatoes produced about 0.6V

In all we had about 3.5V which was enough to light up some of the LEDs we had on hand — albeit dimly!

Conclusion — Electricity is the MOVEMENT of electrons.

We also learned that these electrons move VERY slowly... like the minute hand on a clock, but their 'effect' happens at almost the speed of light!!