Insides of Doc Wattson

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When I was first starting out with the Piaggio conversion, I was monitoring my power consumption using a Doc Wattson / Watt's Up. Good for checking on amp-hours used, voltage, etc.


A few weeks into the conversion, I dropped my bike chain on the Doc Wattson and broke the LCD glass. Very annoying -- they should provide a lexan cover on things like this that will get banged around.

I asked the manufacturer if they did repairs and they didn't. I asked them for the spec on the LCD and they said it wasn't divulge-able. They did give me a discount on my second one and I threw the old one in my "crash" bin.

Well, fast forward a few months more and I've been working with STAMPS and PICs and know a bit more about LCD screens -- especially how most 16x2 displays are driven using the same HD44780 IC chip.

Time to open the Doc Wattson up and see what's in it.

More after the jump

As you can see, the Doc Wattson is two PCBs. The first is the LCD and driver -- standard off the shelf parts. The second (above) is the real heart of the Doc Wattson. It looks like an ATMEL ATTIny26L chip does all the heavy hauling, with a ammmeter shunt right on the board. Very simple and nice design.

The LCD turns out to be (YES!) a HD44780 compatible board, the GM1602H.

I tried jury-rigging a HD44780 that I had, but no go:

But no go, not a flicker (and yes, I know the backlight isn't connected). And yes, it looks weird, but the GM1602H uses a different a different orientation than most other LCD drivers, so the replacement is upside down.

What's up with it not working? Well, it turns out the Gm1602H that the DocWattson uses is a 3.3V LCD driver and most common HD44780 use 5V. So I need to find a 3.3V. Surprisingly, ebay doesn't have any so I'm going to SparkFun.

If it works, I've fixed my Doc Wattson for $15.

More news to come.

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This page contains a single entry by Karen Nakamura published on August 30, 2009 4:43 PM.

Latest photos of Piaggio Boxer EV was the previous entry in this blog.

Piaggio Boxer EV: Revised Bill of Materials is the next entry in this blog.

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