Wednesday, August 29, 2012

Raspberry PI - Home Brew Breadboard

I thought I would make a few notes about the Breadboard that I am using to experiment with hardware and software for my rPI, as it might give some newbies out there some ideas.

Building electronic breadboards is something I have been doing since grade 6 or 7 (in the 60's!) and I find that it is very important to help you build reliable and repeatable prototypes and keep from blowing things up.

If you are trying to experiment with hardware on a table or workbench, you need something plug components into and to hold everything stable. You could use alligator leads and loose stuff laying all over, but if you accidentally yank on a wire it will short or disconnect something, in the worst case blowing up your rPI.
Photo 1

In Photo 1 above, you can see the overall layout. The DVI computer monitor, USB keyboard and USB mouse are on the left. The square frame with really old style plugboard (that used to use very large old components on little frames) came from an old electronics lab in a school that was being thrown out (lab was probably being turned into a "new media room" or something). 

Onto the old plugboard I bolted on an assortment of new style solderless Breadboard / Proto Board units for inserting leaded parts and DIP ICs to build up circuits. A couple of them have been with me so long they are turning yellow! You can get these at any good hobby / electronic supplier.

An old analog open frame power supply that I scrounged from some equipment that was being thrown out by the same school is bolted to the back. It supplies +5 volts at up to 4 amps (see my posting about using a good beefy power supply), and +12 and -12 at 1 amp. It has a power cord that plugs into the 120 volt wall socket, with the green safety ground tied to the metal frame. There is a hole drilled in the wood to run the power wired underneath. Wiring is very simple, if someone wants a schematic let me know.

Photo 2


In photo 2 you can see how I have the rPI bolted to the side so that the monitor, keyboard, mouse and power cables do not move it around. There is a wooden spacer under the inside corner, some insulating foam (just in case, not metal there) and some rubber washers I dug out of my "junk box" to keep trom shorting or damaging the board. The MINI USB power cable goes through a hole on the side under the board.

 Photo 3

 In photo 3 you can see the SPST power switch for the Mini USB going to the Raspberry Pi. This allows me to quickly switch off the rPI without switching off the power supply. Since the PS is analog, it takes a while for the big capacitors in to discharge, and it will run the rPI for quite a few seconds when the plug is pulled out of the wall.

The other switch is a 4 Pole ST switch that allows me to switch off the -12 / +5 / +5 / +12 binding posts with one click, this will be used to power circuitry on the proto boards with jumper wires attached to the binding posts.

You can get toggle switches and binding posts from any good supplier.

 Photo 4

The last photo shows 5 biding posts that have no connection to anything under the board. What I use these for is for connecting test leads from test equipment such as a DVM, Oscilloscope, etc. The leads to them are usually quite heavy, and have relatively thick ends for probing around. I use a banana to banana (or BNC or whatever) lead to connect the equipment, then use a thin long jumper wire to connect to the point in the circuit to be probed. Much less likely to pull something out in the circuit that way.

There is no need to pay someone to cut and strip jumper wires to plug into the proto board, just go dumpster diving and find some pieces of CAT5 solid network cable from an office renovation. Then cut into lengths, strip off the outer sheath, untwist the wires and strip the ends for jumpers.

 To make up the jumpers to plug on the rPI GPIO header, I cut apart an old female DB-25 connector from an old cable (you can find these in good dumpsters everywhere) to get the pins out (hard hacking, but doable if you take care). Then I soldered a jumper cable to an individual pin, covered it in heatshrink, and it's done. You can buy assembled wires with ends, or a fancier breakout cable like this from Adafruit.

I think you will find the time invested in buying a breadboard complete or making one from purchased and scrounged components is well worth the time. It will save you countless hours when your "ratnest" lashup of wires and alligator clips starts to act flaky, or the cat catches a cable and pulls it onto the floor.

Eric Pierce VA3EP - See the Disclaimer in the Introduction

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