Making a gizmo

A Gizmo (or at least the HSA definition) is an electronic device that consists of a loudspeaker, an amplifier and some sort of music player. The device is used to play the sound of hounds 'in cry' i.e. when they're excited and chasing something. Any real hounds in the vicinity want to join in the fun and will head towards whoever is playing the gizmo.

   Making a Standard HSA Gizmo

   Making a Supersize Gizmo

   When things don't work

   Using the gizmo

Our standard gizmo got stolen out of our van, not by local hunters, but by local kids one night who must have mistaken it for the next generation iPod or something. I think a gizmo is a pretty useful piece of kit for any sab group (even after the ban!) so I was keen to replace it. The first part of this article describes how to build a basic HSA-style gizmo but slightly updated.

How to Build a Gizmo

The following table lists the parts (available from Maplin) you will need:

No. Component Maplin Code Cost £

10W 8ohm Horn Speaker 7.99 (XQ73Q)

12W (6-16V) Amplifier  7.99 (N65AW)

12V 1.3Ah Battery  9.99 (MM22)

128MB MP3 Player  24.99 (L05BF)

Car Power Adaptor  8.99 (L17AR)

Car Power Extension Lead  2.99 (BV47)

Rocker Switch  1.99 (N50BW)

Aluminium Box  3.99 (LF16)

 Total 68.92

Before everyone gets up and starts shouting "That's way too expensive!" please bear in mind the the two most expensive components are the MP3 player and the battery. This is a very low spec MP3 player by modern standards so you may find somebody who is upgrading to a better player and is prepared to donate their old one for nothing. The rechargeable battery - if you keep it charged up - will last for 6 years or so which is a lot cheaper than 6 years worth of disposables and how much will 8 NiMH batteries set you back?

The basic wiring diagram for the setup is shown in figure 1. The aluminium box needs a bit of work on it to fit all the components and switches - see figure 2 for the basic positions. It is advisable to lay out the components in the box to give you more of an idea. Get drilling! For the little holes I was using a 4-5mm drill bit. The push button required a hole of 6.5mm. I got the biggest bit I could fit to my drill (1/2") for the really big holes but it still wasn't enough. I spent an hour with a needle file making the holes big enough for the power switch and the cigarette lighter plug. A Dremel drill is recommended for that job!

While I had the drill out I thought it was a good idea to drill a hole in the MP3 player! I drilled a 4mm hole in the battery cover so I could solder wires onto the battery terminals (figure 3). These power leads and the earphone leads (cut off the earphones!) I threaded through into the case (figure 4) and bonded the MP3 player to the back of the case using a 2-part epoxy glue (Araldite or similar).

All the wiring for this project came from the voltage converter which was the next item I butchered! The purpose of this component is to convert the 12V supply from the battery into 1.5V which can power the MP3 player. The cigarette lighter plug is also used so the gizmo can be charged up while driving to and from hunt meets - assuming you have a working lighter socket in your van! Try to keep to the colour convention of black/white for positive leads and black for negative to avoid mistakes. Carefully hacksaw around the neck of the converter just above the tip of the dimple where the neck just starts to widen (so it can be retained in the box). Figure 5 shows how I sawed it a little low down and almost cut into the circuit board! Cut the wires between the circuit board (making the circuit board wires as long as possible) and the cigarette lighter plug. Attach a pair of terminal blocks to the wires connected to the board and add loads of epoxy glue to give strength and offer some insulation without glueing up the free ends of the terminal blocks.

Again like the MP3 player, wires were soldered into the lighter plug to allow it to be connected to the battery inside the box - see Figure 6. That's pretty well all the fiddly preparation done and so to turn our attention to the inside.

The earphone leads are very fine so take care when stripping the insulation back. Figure 7 shows what you should expect to see although the colours may differ. Two wires will be the same colour and these I took as the 'common'. One of the leads I simply snipped back then and used only one pair because this gizmo is mono only. The wires are so fine I connected these to the gizmo (red-topped, push) button. You will need about 3cm of bare wire. The 'common' I slipped under the base of the button and tightened it up. The 'positive' wire I folded a few times and crimped a small red connector over the top. This will clip onto the push button terminal. The positive input for the amplifier was connected to the other terminal of the push button. See Figure 8.

Everything else was fairly straightforward if you know basic electronics and can follow the circuit diagram. I glued the amplifier in place and riveted a bracket to the box behind the lighter plug to prevent it being pushed inside. I only wedged the battery in place (using glued rubber blocks) because after 6 years or so you may want to replace it. The negative battery terminal should be earthed to the case. The power switch should be wired up to allow the battery to be charged in the 'OFF' position and then power go into the amplifier and voltage converter in the 'ON' position. Blue connectors will fit the battery and the power switch. I would recommend using the red bullet connectors to join wiring instead of the blue ones I used for the simple reason that space is tight! Figure 9 shows that everything will fit in the box nice - if not neat!

All you need now is a recording to play - it will take maybe half an hour to download using a 1MB broadband connection.

Supersized Gizmo

To be honest the small HSA-style gizmo was the second one I built and now I'll describe the extreme supersized mother of all gizmos which I built first and has been trialled already in the 2005/6 season with great success. My thoughts went along these lines:

"That's crap - that little black speaker kicks out a paltry 5-6W I reckon."

"Next one down - hmm... that's more like it - a 30W horn speaker!"

"All I need now is an amplifier. Aah, here's an amplifier that kicks out 40W with a 4ohm speaker at 16V. Well, the speaker is 8ohm and if I use a 12V battery that should drop the power down nicely to maybe about 20W - perfect - don't want to overwork the speaker!"

That just about sums up the electronic design work!

The following table lists the parts you will need:

1 30W 8ohm Horn Speaker  19.99 (XQ97F)

2 40W (6-16V) Amplifier15.99 (N67AW)

3 12V 2.2Ah Battery  11.99 (MM23)

4 128MB MP3 Player 24.99 (L05BF)

5 Car Power Adaptor 8.99 (L17AR)

6 Car Power Extension Lead 2.99 (BV47)

7 Rocker Switch 1.99 (N50BW)

 Total 86.93

The horn speaker for this gizmo is massive (figure 10), so to cut down on the bulk, all the electronics fit around the horn. This unfortunately requires a specialist case which has to be made out of metal. If you don't have any sheet metal in your garage Maplin again save the day by selling sheets of aluminium so you can make your own box. The dimensioned design is shown in figure 11. It consists of 2 pieces which can be joined together with self-tapping screws. You will need tin snips or a jigsaw with a metal-cutting blade to cut the shapes out and a hammer to form the pieces.

I used the same basic techniques as previously described with a few notable exceptions:

   This amplifier requires a heat sink and so I used the aluminium case for this purpose and riveted the amplifier directly to it.

   The battery ideally requires suspending next to the horn speaker in this project so it is advisable to rivet some small brackets to the case and zip-tie the battery to the brackets. (Experiment with where to place the battery before fitting the brackets.)

   I used thicker wires between the battery and amplifier because this amplifier can draw 4Amps, so use some 4-5A wire.

   The amplifier was again very straight forward to wire up but the circuit does differ from the smaller gizmo and the circuit diagram is shown in figure 12.

When things go wrong...

So you've put it all together and it doesn't work - don't cry just yet!

   Check your wiring to make sure you have connected each component to the next one in the right order and in the right way using the circuit diagram as a guide.

   Check the connectors are all firmly crimped - the wire should not wobble around in the connector.

   For both the gizmos I built I had problems with the power switches. The power switch doesn't light on the big gizmo and on the small one didn't work at all. To test this out simply bypass the switch and wire up the battery directly.

   Check the battery is properly charged with a voltmeter.

Using a Gizmo

Most sabs have probably used a gizmo before so I won't patronise anyone with explaining the tactics.

   Flick the power switch to 'ON'.

   Switch the MP3 player 'ON' and if it requires it press 'PLAY'. You may then hear a quiet version of the hounds in cry. This is due to the way the speaker is connected.

   Press the little red push-button.

   You may have to adjust the volume on the MP3 player.

   Use the hunting horn and holloa before activating it because it drowns everything else out!

   Keep your eyes open and watch your colleagues and hunters (if any are around) because all you can hear is the gizmo.

   Be prepared to run with the hounds!

Your ears may be ringing for a few moments after using the large gizmo but I haven't suffered anything more permanent than that. You may have to adjust the volume of the MP3 player for the optimum effect. For both of these gizmos I would recommend leaving the power switched on in the field to avoid having to switch on the MP3 player and adjusting the volume every time.

I also recommend fitting a shoulder strap to the large gizmo for the poor fool -sorry- honoured person carrying it around all day. Don't test it out in the van unless you want to cause a crash!

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