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Project Help and Ideas » Program a PICAXE with your nerdkits cable

November 04, 2010
by hapshetsut
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So the question that I think I should first answer is:

"Why bother with PICAXE when you have something as awesome as the NerdKit?"

My answer is simply: Glue Logic. Sometimes when I build a circuit, there are simple logic functions that I want but are simply not efficient to implement in code. Either they take up too much time or too many MCU pins. The PICAXE is an elegant solution in that a) it is easy to program logic in the BASIC environment, and b) you can get 13 pins of I/O for about $7.

Secondly, PICAXE is inferior to the NerdKit in terms of both power and flexibility. But, I can cram a PICAXE on a tiny board if i need to. Essentially, the benefit of using PICAXE is that it can be a reprogrammable PLD or PAL without the time and cost entry barrier of traditional PLDs and PLD programming. Especially since the only startup hardware is a USB to serial converter, which you already have since you bought your NerdKit (you have bought one, right?).

The point of this post, then, is that I wish someone had already made it when I set out to do this.

So, the NerdKit USB to Serial converter is based on the Prolific PL2303 chipset. This is explained on the converter's compatibility page. This is also only important because the folks at PICAXE say their chip is compatible with Prolific Serial protocols. Awesome. But there is one hitch: the output signals are the opposite of what we want! Using the test feature built into the PICAXE programming software, I notices that the Tx output was inverted from what the PICAXE wanted (and, consequently, the Rx output must also be reversed; PICAXE is from the UK, so I guess their electrons drive on the opposite side of the road, too.). This could be changed by altering how the converter works, I figure there is some sort of firmware change that could do it, but then it wouldn't work with the NerdKit!

The first idea I had was to use a 74ls00 NAND as an inverter. Failure. Why? My guess is that the 7400 series chips I have are not fast enough switchers to keep up with my USB Tx output. Maybe a 4000 series or 74HS00 would be, but I decided to change tack. Instead, I wired up a simple RTL inverter. Easily Nimble enough to pace my USB port, and lo and behold, I have a PICAXE programmer, without even sacrificing my NerdKit programmer. The full circuit diagram is below.

It looks easy, but be careful when wiring!

I know this works with my NerdKits cable. Be careful with yours, if you choose to do this. Make sure yours is based on the Prolific chipset! And, lastly, I take no responsibility regarding this! Try at your own risk, I suppose.

April 23, 2011
by DrNoExpert
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What kind of picaxe are you programming? I tried the same thing with both IC and RTL, and I still could not program it. Are you also programming from the picaxe programming editor or programming it via another software?

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