Ghettotronics

ghettotronics

gɛtəʊˈtrɒnɪks/

noun

1. The branch of physics and technology concerned with the hacking of circuits using 

sub-optimal equipment. Typically carried out in a shed, spare room or somewhere else equally unsuitable for the task at hand.

Quite often when messing with electronics you get to the point where doing something is either too expensive to do properly or too hard to cheaply. For example, you could precision laser decap a chip you want to reverse engineer or you could throw some acid on it and hope for the best. You could buy a multi channel logic analyser or you could try and build one using your spare arduino. You could invest in a rework station for removing chips from a circuit board or you could just try your luck with your soldering iron.

The cheap and probably-going-to-fail-but-fun-trying approach is what I call ghettotronics and I seem to spend a significant amount time involved with it. 


A recent example involved wondering how to sniff a TSOP package. I didn't actually have a requirement to do so at the time, I just wanted to know how to do it in case I ever needed to. Here is a picture showing a SDRAM chip inside an old router.

The yellow wire is just a normal breadboard jumper to give a sense of scale.

I suspect with a healthy does of luck I might be able to solder a wire on that wouldn't cause a short but I also wanted to try and be as non-destructive as possible so I started thinking about an alternative approach. The first idea was to build a jig but frankly I'd still have the issue of aligning and holding contacts on the pins so that was ruled out. My second idea seemed good in theory so I gave it a go.

Hot glue. It rocks. The plan was to smother one row of pins in hot glue, allow it to solidify then peel it off gently. In theory I would have an exact template with little grooves where the pins sit. I would then insert a single wire strand into the groove of the pin I was trying to tap. As long as I also covered the corners of the chip I would also be able to align the blob perfectly. 

Sounds great in theory but this is what the end result turned out like. The idea was to hook the tap wire onto the clock pin just to verify the signal was being picked up correctly.

This is what it looks like when mounted on the chip. The red wire was just a convenient ground point for the scope. The tiny wire sticking out of the blob should have been the clock signal, but it wasn't. It looked a bit random to be honest. I'm pretty sure I was nowhere near precise enough when making the hole for the wire and despite it being a single strand it probably is still too wide.

I'd be interested to hear how others go about sniffing chips with tightly packed pins or if it is just a case of desoldering then resoldering back onto a dedicated test board.

Anyway, there is plenty of room for improvement with this technique. I'm not sure it is quite ready for the scrap bin yet. Of course, a Mantis Elite might have made life much easier, but that wouldn't have been very ghetto, would it?