After last week's failure, I went back to the drawing board for the buzzer system. The problem was it wasn't loud enough in the water. So this time I popped back to Maplins, got a few more bits a pieces, and knocked a new buzzer unit up. As you may recall, last time I used a BDH with a two-tone 105dB (@ 1 metre) piezo sounder. Well, this time I swapped the BDH (which is basically a cylinder) with a square not-quite-waterproof (only IP56 rated - ie splashproof) plastic box (which was subsequently sealed with silicon sealant). This time one piezo siren was glued into the lid (where it fits diagonally), and a second was badly butchered, just to keep the circuit and the two piezo units mounted in their acoustic chambers, which were glued to the side of the box. The idea being that twice the number of sounders is bound to be better, and by glueing them directly to a fairly rigid plastic surface (rather than a rounded, soft plastic tube in the form of a BDH), the propogation of the sound into the water should be better.

The result? Firstly, it's waterproof. Although we didn't use it much, I left it in the pool the whole session, and no evidence of leaks. As for the sound, it's better. It's not perfect, but with the unit placed on one wall in the centre of the pool, it's audible in the far corner. Just.

Next step is to build a second unit - the control box was always designed so that two sounders could be run from it, just in case. Then I'd put one sounder at each end of the pool, behind the steps, which has the added benefit of ensuring the box doesn't get kicked, dislodged, or anyone get tangled in the cable. Unfortunately, I've pretty much run the local Maplins out of piezo sirens and waterproof cable glands, so it looks like it'll have to mail order next time. Oh, and the costs are going up too. I'll try and take photos when I built the next sounder unit, and post a full parts list and set of instructions. And a list of other things I want to do to improve it further. Oh, and I might also try using the BDH, but with a car horn instead.