ELECTRONIC CRICKET
REINVENTING THE GAME OF SPOTLIGHT
The editor and I were discussing articles for this issue and we both decided that something fun would be the idea. Fun always sounds good to me.
A couple of days later I recalled a project that I’d seen way back in my scouting days, where we went hunting for an electronic cricket. Someone would head out and hide the device and after some time (to allow the valves to warm up) we’d head out into the park to see if we could find what was making the chirping noise.
Searching the www (Wonderful World of Wacky) leads you to all sorts of things and the choices came down to either buying one, making one, or buying a kitset. Luckily the local electronics store had two kitsets — Jiminy and Clifford — and they had different features.
What is an ‘electronic cricket’?
For anyone who isn’t familiar, these are a small, battery-powered object that sit and make annoying noises. Some have a light sensor, so that when you’re searching in the darkness with a torch trying to find it, it will detect the light and go quiet.
I’m not sure how the Health and Safety (H&S) people would regard this, as it encourages you to walk around blindly, trying to find something that is hidden, for no reason other than a game!
The other version reacts to sound, which may be more suitable for the H&S people.
Since the readers of The Shed are quite
Luckily the local electronics store had two kitsets — Jiminy and Clifford — and they had different features
capable of making their own judgements and ignoring the modern world of PC gone wrong, I’ve detailed both versions.
Kitsets
These usually have everything you need to make the item, and this extends to the instructions, solder, and wire to connect the parts, so it’s a great way to make something if you don’t have a shed full of electronics.
For anyone not used to soldering, I suggest checking out our Soldering On article in Issue No. 77, March/April 2018, and have a practice.
Jiminy is based on a published article, but you can download the instructions from the download tab here: jaycar. co.nz/short-circuits-book-volume-ii/p/ BJ8504. It is on page 92, but it is worth looking at some of the other handy hints and tips they have on pages 8–18.
It’s obvious to start with the board and usually the resistors are the lowest height component, so they go in first. Resistors use various colour bands to create a numbering scheme, and I’m not going to repeat the mnemonics phrase we used to remember the order. Luckily the instructions for Clifford have the colours listed, but they don’t mention which end to start with.
I suggest picking on the value that uses three, and you see if you can match the colours.
Those were the days
Modern maths has a lot to answer for because in our day when you wanted to multiply by 10 you simply added one zero to the end; multiply by 100, add two; 1000 was three, etc. The resistor multiplier is the same — add xxx zeros to the three numbers, and you have your resistor value.
I suggest starting with the multiple values and fit these, then working on the single resistors. Cut them off the tape, and bend them to fit the board. It doesn’t
It encourages you to walk around blindly, trying to find something that is hidden, for no reason other than a game!
matter which way you insert them, but it is neater if they are all facing the same way.
As you insert each one, bend the leads 45 degrees to hold it, then insert the next one.
We tend to find that the students get the 4K7, 47K, and 470K mixed up, so if you have a hole that is not right, go back and check.
Eventually you will have placed all the resistors, but before soldering them, take another look and make sure they are right, as it is much easier to fix mistakes before you solder them in.
For whatever reason, they mark the negative lead on a capacitor and then mark the positive hole on the printed circuit board (PCB). I’ve never understood the logic behind that, but they do need to be inserted the right way.
LEDs also have a polarity and they have a flat on one side. The positive (anode) lead is longer, but relying on this is only useful while it hasn’t been trimmed, so try to identify the flat side (cathode).
You may notice that the board seems to have extra holes for the capacitors and transistors. This is simply to allow the suppliers to provide a different case or style, and it saves you having to bend the leads, so choose the holes that allow it to fit flush with the board.
Beware the magic smoke
Eventually you’ll end up with a board that has all the passive components fitted and soldered. It is now time to add the integrated circuit (IC). You’ll notice that its legs are splayed. Rest it on one side and push it towards vertical to bend the leads then repeat with the other side. This will make it fit the socket or holes. Do ensure that the notch is facing to the notch mark on the outline, otherwise it will release the magic smoke and stop working.
Clifford came with a socket for the IC, and it’s important to mount this flush with the board. Insert it and bend one lead at diagonally opposite corners, solder these, and while holding it with one hand, apply gentle pressure to the socket and reheat the leg. Repeat with the other and once it’s flush on the board, solder the rest of the pins.
The piezoelectric speaker has a sticker covering the internals for automated assembly, and you can remove the sticker at any stage. I left the lightdependent resistor (LDR) leads long and bent them to make it face forward.
Jiminy has a normal miniature speaker. Don’t solder to the existing solder, as this is the fine wire from the coil and can easily be broken, so add some solder to the outer edge, and solder your wire onto this point.
The electret microphone has a positive and negative, and the guide shows the negative connects with the case. I carefully bent my leads to allow it to mount on the PCB and face outwards.
I did have thoughts about not adding the LEDs, but Clifford’s design uses these, so if you don’t want them, they need to be covered. Feel free to ditch Jiminy’s, or just the 2K2 resistor next to Q1.
Time to test
The moment of truth is when power is applied, but before you add the battery and wonder, “Will it work?” take the time to look carefully at the underneath for any soldering that you missed, or worse, over soldered and accidentally joined to the part beside it.
Solder the one you missed, and fix the excess using the techniques we talked about on page 84 of the Soldering On
If everything looks OK, then add the battery and wonder at this thing sitting there making some form of noise and flashing its LEDs
article (Issue No. 77, March/April 2018) using your local gravity to assist.
If everything looks OK, then add the battery and wonder at this thing sitting there making some form of noise and flashing its LEDs.
For Clifford, if you cover the LDR it should start making noises, or, alternatively, shining a light will make it go quiet. You can add a tube over the LDR to make it directional and the sensitivity is controlled by the 47K resistor at the end of IC1.
Jiminy on the other hand seems counterintuitive. Rather than making noise when it’s quiet, this one seems to come alive and make noise when there is sound. I guess he thinks he’s joining his mates.
Housing
The idea of these projects was for just fun, and I can imagine a game where someone hides them and then the kids go searching for them.
You can use these indoors, but it is a much more fun exercise trying to find these hidden in the backyard, or when you’re camping somewhere. To hide and protect them, I chose to use an old tin as a shelter. A piece of foam on the underside and a cable tie to hold it in place stops it shorting out, and an elastic band holds the battery onto the foam and helps save the connections from breaking.
I can imagine one of our readers creating a giant weta-like creature with this buried in the internals, but the point is it doesn’t need a complicated housing, just something to protect it from being trampled while people are trying to locate the source of this noisy creature.
Enjoy your cricket and have some fun with it.
You can use these indoors, but it is a much more fun exercise trying to find these hidden in the backyard, or when you’re camping somewhere