Hayling Island

Hayling Island

Saturday, May 10, 2014

More soldering pencil fun ..

I was playing with the Hakked Weller soldering pencil, and decided that I really need to leave it alone and play on another prototyping board. You see, the thing is that there isn't a lot of room inside the Weller case for experimentation, so now it's working OK, I want to build another one for playing with.

I've got a few NEC VFD displays from a retail project I was working on, and I wanted to join that together with an Arduino base. So, I made up a nice PCB for it. Another nineteen dorrar down the drain.

Schematic ..

Just a regular 328P processor layout, with a 26-pin connector for the VFD; a filter with a gain of about 23 for the PTC element in the solder pencil, a pot to set the desired temperature and a driver for a logic triac. The whole thing runs off a 12-0-12 2A transformer, and I have included a switching PSU for the +5v, and a linear regulator for the -5v. Actually there is a -15v supply hiding near the triac driver, since the triac gate is driven by current flow, and the current flow needs to be between MT1 and the gate so the 'ground' for the driver needs to float about 15v below the voltage on the MT1 gate.

And now I am testing out the result .. so far, so good but the triac driver is causing some concerns. I mean it works, but it's messy. I have a real opto triac driver coming from China soon. I can't bring myself to paying UK prices, when they are for one off, twice the price of five coming from China. AND I have to add postage to the UK one.

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