I want to use this thread to share my extremely tortuous progress in what I laughingly call “fast prototyping.”
Why do I call it fast when it takes so long? Well, it’s all relative. I seldom have both the time and the energy to do much, and my days are so exhausting that I spend most of my little spare time relaxing in bed. There are times when I’m in bed because it affords me some space where I feel relatively safe from the duties of the day, but for a short while I’ve got enough energy to post to internet forums like this, and it turns out that those times are my most creative.
So I’ve evolved towards selecting techniques that, while not optimal, can be used by a person sitting up in bed. Here’s an example of what I mean. I did this just now.
I did this while sitting up in bed. That’s one of my A5 3mm greyboard panels. I bored a crude hole and used it to mount a banana jack. That edifice towering over it is the 1:4 passive multiple built out of banana plugs.
One of the plugs has a small length of hookup wire protruding from its rear. That’s from my successful test to see if the banana plugs could accept wire as thin as 20awg.
Here’s the rear of the same panel. It shows my successful experiment in using ice lolly sticks epoxied to the greyboard to provide a stiffer panel medium. Successful but mostly unnecessary, because 3mm greyboard is satisfyingly stiff at A5 dimensions.
One thing I’ve learned from this is that I may want to leave quite a bit of space around output jacks to allow for chaining of multiple banana plugs. Another thing is that, because the panels aren’t as firm as plywood or most metals, I have to brace the panel with a finger as I remove a plug. The panel itself can handle the strain of pulling the plug out, but I think it’s likely to cause wear in the fixing between the panel and the case unless I use that technique.
Overall I’m impressed by the ease of this evolving prototyping technique. I can bore a suitable hole and mount a jack or potentiometer in a couple of minutes, the material costs are tiny and my failures can be put into the home recycling bin. Standardising on international paper sizes means I can concentrate on getting the layout right, and when it works I can easily switch to wood or any other material available ready cut to those sizes.
I also want to summarize my overall impressions of Kosmo-style 6.35mm mono jacks, banana jacks and the 3.5mm mono jacks used with my Behringer Crave and of course with Eurorack.
Aesthetically, there is no question. The big jacks win that round by a mile. I’m with Sir Mixalot on this. Baby Got Back.
For practical purposes, though, smaller jacks make more sense in consumer electronics. With well spaced knobs and switches, the Crave (and its inspiration the Mother 32) provide about 30 3.5mm jacks on a small panel, in an instrument smaller than a laptop. I wouldn’t want to live-patch a panel this tiny but it’s a perfectly acceptable trade-off for an instrument that will find its place mostly in home studios.
Only slightly larger than 3.5mm mono jacks, 4mm banana jacks are electrically and mechanically much simpler. There is only one conductor and no switching.
This has some disadvantages, for instance your electronics needs to be designed to handle floating terminals sensibly, and you can’t incorporate a “normalling” feature into the jack itself. In the worst case, you may need to provide a separate panel switch.
On the positive side, this simplicity appeals to me aesthetically. The second conductor used in 3.5mm and 6.35mm mono patching is unnecessary if your circuits are designed properly, so why cater for it when a mechanically and electrically simpler alternative is available?
I’ve yet to test whether this notion, currently no more than a hunch, bears fruit in practice. I suppose I’ll find out when I start connecting my microcontrollers to this switchgear.
Each of these banana patch cables on the left took about two minutes to assemble with my clumsy old geriatric fingers. No soldering was involved. A 3.5mm stereo jack moulded audio cable is shown for scale.
The cost of the plugs is about 20p, making 40p for the pair. The cable body is 20awg insulated stranded single core wire I bought to use as generic hookup wire. At £15 for seven reels x 7 metres it works out at 30p per metre. The panel jacks I’m using cost 20p each.
Next, I needed to cut a 12mm by 6mm letterbox slot for a Grove I2C connector. I used an old not very sharp Stanley knife, and a small rule and pair of scissors from a SwissCard multitool I carry around in my card wallet. I put the slot in the wrong place so the Trill Hex sensor overhangs the edge of the panel, but I’m satisfied with the speed and ease here.
There’s a tiny amount of surface mount circuitry in the rear of the Trill sensor, but it’s designed to lie flat and I found that the snugness of the fit to the slot I cut was enough to hold it quite well.
I might use blue tack or some other temporary adhesive to hold the sensor more steady. Once the Grove connector slot is there you can replace the Trill Hex with any other Trill sensor such as the Trill Ring. Anything that will physically fit into the space in your panel can be connected through that slot.
Grove is a very simple quasi-standard that’s popular with Arduino and other robotics platforms. It officially supports digital I/O, analogue I/O and I2C and it can be used for a lot more. The provided cable here converts the four pins of the Grove connection to four plugs that fit female headers. You’d plug them into your Arduino or whatever board so as to enable the board to talk I2C to the sensor.
I like collecting prototyping methods! This one guy showed me how he uses plain copper clad board and a knife to make fairly high performance switching supplies. There are so many ways to build stuff.
It’s not absolutely necessary, but using a two conductor lead for patching allows for ground to be run with the signal to provide a signal return path. This can reduce noise.
I’m going to be carefully evaluating the performance of different kinds of jack in my prototyping system. That’s one of the first things I’ll do. I’ve got a number of different microcontrollers and Systems on a Chip and, as you can see above, different sensors to attach to them. I’ll want to look carefully at the amount of noise that appears in my audio lines. It’s all part of the fun.
This new, thicker patch cable is 14awg, a gauge commonly used as speaker wire. Speaker wire is two-core but usually easily splittable down to two distinct single core cables. Amazon sells 14awg speaker wire at 70p per metre. If you split it out the cost is 35p per metre, close to the 30p per metre cost of 20awg hookup wire.
I really like this approach but know sod all about how the lack of earth in the cable is compensated for. Or is it? Who’s our banana man? How does this work and what are the tradeoffs?
Getting back to fast prototyping I am a huge fan of dead bug construction and 3d builds. Vox made beautiful blocks of circuitry in the 70‘s for on board fx. Moving a layout piece by piece off a breadboard and soldering the parts together directly is great fun and quick.
The signal only needs one conductor. To travel along that conductor (the banana cable) the signal needs a path to earth (or ground, if you prefer.) All you need is for the source and destination of the signal to agree about what earth is. The simplest way to do that is to have an earth terminal on the interior of each module and have all the earth terminals wired together.
If you want to introduce a Kosmo patch signal you have to have an adapter, which can for instance be in the form of a 6.35mm jack that takes the ring to earth and the tip to a banana jack from which the signal can be patched to its destination using a banana cable like the ones I show in the pictures above.
The biggest attraction of this, for me, is that I get to make up my own patch cables for pennies and it takes a couple of minutes (or less) with a wire stripper and a screwdriver.
The incoming signal current doesn’t really care where it came from; it’ll take the shortest route back to the power supply’s 0V rail. Which is usually via the power rails, not the signal cable it came through.
(well, technically speaking the electrons come from the 0V rail, but that’s physics, not electronics).
Things get more complicated if you have bigger systems, with multiple power sources. You need to make sure that they all agree on where 0V is, which can be trickier than it sounds.
The more I think and read about this the more im eager to use something like this for one of my boxes. Looked at banana plugs which are fairly cheap and then, being Scots, thought “could I do it cheaper?”
Planning a test soon with m3 nuts, bolts and plastidip (my new favorite alternative to heatshrink).
The issue of multiple power supplies will be a problem if I want my boxes to interact. I know only too well from touring and a different pa every night, sometimes having to remove earths from my amps. I cannot even begin to think how I’ll solve/make safe but it’ll be fun or Smokey finding out.
Here are two identical patch cables made by splitting about 1 metre of two core speaker wire into two single core 14awg insulated lengths and screwing a banana plug on each end. I find making up patch cables very enjoyable. Does it show?
I am serious. I’m even thinking about battery terminal springs and no plug at all. Though being a Scots issue is a joke and is more about creativity, uniqueness and good design.
I do! Especially when I miss out more than one key word in a sentence. Sorry about that.
So in Summary.
Scots are not miserly.
I am more than somewhat eccentric.
I admire the approach you are taking and am imagining how far you could take it.
I would use wooden clothes pegs and string if it looked good and conducted a signal.
“Load of Kelvin sometimes”. Plural, really? Thanks for that mate. Im touched.
Sorry I think I said something offensive when I was aiming for funny. I’m utterly fine with your English. I was trying to make a joke about famous Scottish geniuses.
