Latching Relays are the answer

I have spent ages during this project trying to make simple coin operated devices.  I thought, wrongly, that channelling a coin down a route which meant it would straddle a gap between two metal contacts could reliably complete a circuit and whatever device was within that circuit would be turned on, albeit momentarily.  A day spent wobbling bits of metal together showed this theory didn’t work.. a switch needs to have a much more definite controlled action, the contacts I was making sometimes worked but generally did not. 

Tim Hunkins website provided the answer here .  The long wire movement operated switches were the solution I needed, switch number 339-207 from RS components (about £3.20).  This provided the means to reliably switch on anything by dropping a coin through a slot (1p, 5p and 20p less consistant than larger coins).  This enabled the 20 second recording modules purchased from Rapid Electronics to work inside my donations boxes.  The link to the part number for these is here (about £6.50).  I cut the leads to on/off button and wired them onto the terminals on the wire movement switch.  The speakers are small and rubbish sound quality, so for most of these units I have replaced them with small mylar speakers VC86T purchased from Maplins (£2.50).  This has enabled the simplest element of the project to be realised, donation boxes that come with sounds attached.

However, a momentary pulse of power as supplied by the activation of the wire switch is far too brief for any motorised action to take place.  The solution, after mucho head scratching (mostly the cats heads), I reread a book titled Cabaret Mechanical Movement by Aidan Lawrence Onn & Gary Alexander.  In their book (on page 105) they talk about the need to build in a latching relay circuit.  Well I took the book to Maplins and explained I wanted a relay to make a latching relay circuit, and they didn’t have a clue what I was talking about!  However, thank God for Ebay, where I did find what I was after: NAIS DR L2 3V, five for £9.85The next issue was how to wire it up.  These relays need to be soldered on to copper strip board as there are 8 tiny pins and no way to anchor the slippery little things.  My soldering is now much better than it used to be!  I blew up the first relay as I put 6v through the coils and I noticed after a while the relay was getting very very hot and didn’t work..I had wired it wrongly as I didn’t understand how the switching was supposed to happen!  I had to consult guru John Philip for yet more help and he drew me a diagram.  When I followed his instructions with a new relay it all went a lot better and finally I had movement.  Below is a photo which includes the latching relay, the vero board with terminal pins all soldered on and the coin trip switch recommended by Tim Hunkin.

and here is John’s wiring diagram showing how a smaller voltage works across the two coil switches and a larger voltage through the motor.


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