Lamp Board
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(Initial creation of the page with board description and write up of LED modification.)
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Revision as of 20:35, 29 April 2007
The blinking light on the top of the RoboMower is handled by a small circuit board containing a light bulb and a resistor. Various models have used different light bulbs; some with a screw-in socket and some with a bayonet socket. All use a 24v bulb and a 20 ohm, 1 watt resistor. Pin 1 on the board is positive.
There is lots of room in the top light compartment. This could be a good place for hacking in something fun.
User:Dougs: I replaced the light bulb on one of my mowers with two bright white LEDs. I just grabbed parts locally from Radio Shack. The LEDs are part number 276-320, which are rated at 3.6v and 20mA. Doing the math (here's a nice online LED resistor calculator) tells us that for two LEDs we need a 1k ohm, 1 watt resistor, which Radio Shack has as part number 271-153.
There are two reasons I used two LEDs. First, LEDs are very directional. By using two pointed at opposite angles it's easier to see them all around the mower. Second, two LEDs dropped enough voltage to get to a resistor value that Radio Shack had in stock.
I used some solder wick to remove the old light socket and resistor from the board then installed the new components. The short lead of the LED, usually near a flattened side is negative, so that goes in the hole nearest the connector. You can see the circuit trace from that hole going to pin 2. The longer lead of the other LED goes in the other hole left by the light socket. Then the other leads from each LED are soldered together and clipped short.
The results were very good. I would say that the brightness is close to that of the original light bulb. It does have a slightly different color to it and is brighter when viewed from the sides where the LEDS point.
I will modify my next mower light a little differently. Radio Shack parts tend to be quite expensive so I'll order everything elsewhere. I'll also use a wider viewing angle LED, which should appear brighter overall. The B322 from BestHongKong.com looks like a good candidate with a 120 degree viewing angle at and about 1/10th the Radio Shack LED price. There are also some good choices at super Bright LEDs and Mouser.
The other thing I may do is see if I can raise the LEDs up a little higher. There's plenty of room in the compartment and that should help make the light more visible.
