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The $10 Digital Counter

Now this sure isn't one of your step-by-step how-to stories.

by Julian Edgar

Click on pics to view larger images


If the idea of thinking laterally and creatively gives you a headache, press the browser's 'back' button.

Right now.

Uncertain? No, go on... do it! Go read a lightweight story...

But if you're the kinda person who likes to grab the germ of an idea and run with it - this is for you.

So what am I on about? What we have here is a digital counter, a device which can display a count-up in response to an event happening.

A bit obscure? OK, let's say that you circuit sprint your road car for a bit of weekend fun. The tightest corners are left-handers, and you're pretty convinced that your right-rear is bottoming out several times each lap.

Oh yes, so is your car's suspension.

Click for larger image

While you think it might be happening pretty frequently, maybe it's occurring only once per lap? How do you find out? Well, it's easy. With our famous $10 Digital Counter and a simple $2 microswitch, you can count exactly how many times the full suspension travel is used up. Just cable-tie the microswitch on the suspension somewhere so that it is triggered on full bump, and connect it to the $10 Digital Counter. Press a few buttons, head out onto the track and when you come back to the pits and have time to draw breath, just read it off on the display.

That's just one use - I'll come back to some others a bit later.

But what's he on about anyway? Just what is this $10 Digital Counter? After all, a decko at the pic at the top of this screen could have you believing that it's just a calculator - one in this case with the pretty pleasant name of 'Garbo'! Well, it is. Nope, not a Garbo - well, it is indeed that in name, but not in function - but a modified calculator. That's why it's just so damn' cheap.

But you can't use just any old calculator. No, my golly gosh, no. It needs to be a special calculator...

Buying the Calc

Now since this is the single big-ticket item on the shopping list, select it with care. After all, a $12 calculator will blow your budget by a massive 20 per cent.... But as well as the financial outlay, you also need a calculator that functions in a particular way. And not all calculators do - function the right way that is.

Click for larger image

Don't believe me? OK, grab the nearest calculator. Turn it on, then press "1 + 1 =". Yeah I know that every calculator will now display "2", except of course those obscure Hewlett Packard designs with Reverse Polish Notation - but if you own of those you are a dork, dweeb, wear thick glasses, did a B Eng at uni, and basically should be able to design and build your own digital counter out of a packet of matchsticks and a single banana. OK, so for those who don't own a calculator with a weird 'Enter' button, you'll now have pressed "1 + 1 = " and be staring down at "2".

And now here's the tricky bit. Without doing anything else, again press the "=" button. What happens? On some calculators, the answer will stay at "2". If your calculator does this, take it out to the shed, select a large hammer, and destroy it. It's not the type you want. But if your calculator increments to "3" - and then when you press the "=" button again, to "4" - congratulate yourself as you have the right design.

Cos you see, all that you need to do to make this type of calculator into a digital counter is to make the 'equals' sign operate every time that you want to count up. Easy, huh?

This sorta Digital Counter Functionality (DCF) kind of test is easy to do in the shop before you splurge your last hard-earned, too. Like, with the superb pictured Garbo (being sold from the counter of a petrol station) I tested out its DCF in front of half a dozen indifferent customers, the console operator, and the knowing eyes of the semi-naked women peering out from the covers of four cylinder magazines in the display rack.

And while you're checking the DCF, also consider a few other desirable characteristics. Firstly, does it look like the calc pulls apart relatively easily (eg a few Philips head screws in the back)? And, if you wanna get real tricky, is there a 'beep' function each time you hit a key? The - ta da! - wonderful Garbo has this ability.....

Modifying the Calc

Once you've done the DCF test and found the C of your dreams, it's time to convert it from being just a C to a DC. But first a vital step. Grab a sheet of paper and make a quick drawing of the face of the calculator, showing where each button is. Why? Cos if you don't do this, it's a helluva laugh trying to find out the location of each button when you're re-assembling it. I didn't do the drawing and it took me about half an hour of determined trial and error...

('Course, this is also a pretty fun way of deliberately stuffing up someone else's calculations - you can now get your new car financial sleight of hand past your partner just by getting her to work out the figures on your new - surreptitiously modified - calculator!)

Click for larger image

But for DC uses, make the drawing. After that, disassemble the calculator, revealing the copper tracks that lie behind the keys - specifically the "=" key. You'll soon see that when the button is pressed, its graphite rear coating bridges the path between two different printed copper patterns - in other words, pressing the button closes the switch. Using a very fine soldering iron and thin insulated wire, solder a wire to one of these conductors, and the other wire to the other conductor. This means that when you join your wires together, you are performing the same operation as pressing the "=" sign. If you are very careful where you solder the new wires, the calculator's own "=" sign should still work OK as well.

Make a small hole for your wires to escape from the case and then re-assemble the calculator. Check that all the keys work as they should, then do the DCF test ("1+1=") and touch the ends of the two wires together. The screen should then change to '2', and then each time that you join the wires, the DC will count up another unit.

You've just built a digital counter...

Using It

There are two ways of triggering the Digital Counter.

A switch that closes each time an event occurs (eg the microswitch clicking when the suspension reaches full rebound) can simply be connected straight to the Digital Counter input. However, if you want to count whenever something is turned on (eg an intercooler water spray pump) then you'll need to use a 12V relay. Connect the relay's coil in parallel with the load (eg the pump) and then connect the relay contacts to the Digital Counter so that the counter is triggered each time the relay turns on.

Using a switch input, here are some uses I can think for the Digital Counter:

  • Full suspension movement events (bump or rebound) - using a microswitch on the suspension.
  • Low oil pressure events (eg on the track) - using an oil pressure switch
  • Count how many pedestrians walk across in front of you at traffic lights - pushbutton input
  • Boost events - using a pressure switch (To wife: "I told you not to use any boost and you have got boost 25 times just on the bloody trip to the shops!")
  • Lap counter - press a switch each time you do a lap so that you actually remember to come in when you're supposed to.
Click for larger image

Using a relay input you can count:

  • How often the intercooler water spray operates - relay wired from pump control wires
  • How many times you brake - relay wired from brake lights
  • How many times the left indicator flashes (why? - who knows!)
  • How many times the radiator fan operates - relay wired from fan power

But this is just scratching the surface. There are a heap of other uses! What, you ask? Buggered if I know - but that's why I said at the beginning that only lateral thinkers need keep reading....

And the real bright sparks amongst you will have realised two things:

You can use the DC as a countdown timer. Just punch in (say) "100 - 1 =". Then it'll count down from 100 to zero. Er, actually it'll happily go into minus numbers as well...

You can add or subtract numbers other than '1'. In fact, if this was a website devoted to surveying, I could tell you how to make a linear distance measurer by using a reed switch and a magnet that passes it each time you wheel a bicycle wheel forward one circumference. And that circumference can be 1.135823 metres if you want....

Plenty of stuff to be thinking about!

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