Bench Power Supply

Many years ago when I first started to study electronics I a reasonable selection of test equipment and a bench/workshop in a spare room. Much of this equipment was bought second hand from college or out of the free adverts in weekly/monthly trading newspapers.

I long ago abandoned much of this equipment, when I moved out of my Camden flat to buy a home in Bishop’s Stortford. The remainder of this equipment is still in service but has seen better days.

One of the casualties of the move had been a very heavy yet very sturdy variable bench power supply. Since then I had built a power supply from a modified old computer ATX supply. This work really well until it suffered fluid ingress.

My better half splashed out this year and helped me to buy a nice new bench power supply! As is the way with many things these days it can be linked up to a network or to a computer via USB. This has the advantage of offering better control options then the front panel buttons. It has some memory functions enabling quick setting up of common voltage and current options. It also allows for sequenced switching of power settings and recording of the power used into a table.

In addition to the 2 variable output channels a 3rd channel allows switching between 2.5 volts, 3.3 volts and 5 volts at 3 Amps.

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Heater repair

While trying to set up some lamp controllers for work purposes, I grabbed a fan heater as a load. I forgot to put the unit on fan only mode. The controller could not handle the load and so was oscillating and the heater was not getting cooled enough by the fan so it soon overheated. I may have noticed this before damage had been done, had I not been full of cold.

By the time my partners nose was provoked into asking me if I was letting the smoke out of something, it was too late. The plastic case had suffered some melting and the thermal fuse had blown.

I sourced some from a well known auction site 5 for 99p type of deal. These were wire wrapped over some brass clips. I have just done the same.

Thermal Fuses same rating different colour.
121 degree Centigrade 10 amp ere thermal fuses.

Thermal fuses fitted were RY121 Bayle. These are 121 degree Centigrade 10A. The replacements had a different colour cap but the code was the same and are still 121 degree Centigrade 10A rated.

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Joystick Thoughts

When I first chose my Joysticks I had decided on the Sanwa JLF-TM-8T which has micro switches with Common, Normally Open and Normally closed connectors. Theses seem to be continually out of stock so I settled no the Sanwa JLF-TP-8YT which has no connection to the Normally open available at the micro-switch. It has the common linked through on PBC that the micro-switches sit on, while this cuts out some wiring it does mean that my original plan for mapping the buttons will not work as not all the switches were common to the same control wire! My choices are to interrupt the circuit board and solder wires to the switch contacts or to remap the planned switch contacts.

For now I will go with choosing another layout for mapping the USB encoder. If I decide I do not like it then I will modify the joysticks as required.

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Player 1 Test

Using a bunch of spear wire from a old central Locking kit, I have tested the Encoder for player 1. It works fine though the number lock is activated as indicated by the led on the encoder pcb.

I probably will not used the current setup of buttons and may have to rewire the buttons that I daisy chained as they are using the same control wire on one side of the switch.

A friend of mine has a spare control panel that I could have done with to keep things neat, but a planned visit to see him did not happen.

My next step is to wire up a second set of buttons and a joystick for player 2 and make sure I can get them both working from the one keyboard controller on Retropie.

A friend of mine told me that the Pi 3B+ does not like having 2 keyboard controller connected and that the Bluetooth Keyboard I was intending on using for non programmed functions on the final machine, may conflict!

I will test this at some point, but if it is a issue I have the option of setting things up by SHH protocol over the network.

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USB Keyboard Encoder Interface

I located some old strip board on which to terminate the USB keyboard encoder taken from an spare keyboard. The strip board had previously been used in unfinished project as a cartridge port for one of my Synthesizers, so it had a 30 pin female header attached. I could have used this to plug in the USB encoder PCB, but elected instead to fit a male 30 pin header to the PCB and then terminate the 27 control wires from the USB Encoder PCB to female header sockets. This way it can be unplugged to allow additional PCB connections to be made or swapping out of encoders if the need arises.

Old Strip Board
Old Stripboard

The sockets are arranged form 3 time 9 pin sockets and a 3 pin socket. The 3 pin socket is purely there as a spacer and is intentionally left devoid of wires. One of the 9 pin sockets contains a ground connection and 8 wires that attached to one side of the original keyboard membrane. I have called these A1 to A9 in my matrix.

The other side of the keyboard membrane consist of 18 contacts B1 to B18 in my matrix. This is formed of 2 more 9 pin sockets.

USB Encoder
UBS Encoder Terminated

Obliviously this could have all been made much smaller but as it is all going in a full size arcade style cabinets eventually, so I left it all as is.

I have mounted the USB keyboard encoder onto the interface PCB using a couple of standoffs. Rather then disturb the straight though strip board connections drilling mounting holes, I simply used a glue gun to mount the standoffs to the strip board. I also used the glue gun to dress the USB cable.

While I could use the remaining header socket to my joystick and control buttons. I figure that it might be desirable to be able to easily terminate one or more wires bu screw terminals. Particularly while testing. So at the opposite end of the PCB I have added PCB terminal blocks. I have organised these to cover just the 27 wires used in the Encoder. As the pitch of these is terminating a every other strip board track, I have staggered two sets back to back. These Organised as odd numbers and even numbers, 2 time 9 terminals for the “B” matrix connector. Then a 5 odd numbers terminal and 4 even numbers terminal for the 9 way “A” matrix connections.

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Keyboard Encoder Matrix

I have mapped the contacts from the encoder circuit board to a matrix.

My first attempt was incorrect in that I had counted the black wire A9 in my matrix on closer examination it is a ground wire and not directly connected to the keyboard membranes switch contacts.

I had seen it suggested to connect the keyboard encoder to a computer and then use “Note Pad” or a similar program to show the character that appears on each linked pair.

I elected to hook it to the “Retropie” and list what came up in the Controller setup screen. This proved to be a very effective way to chat the outputs, but it did require multiple resets to complete all the combinations.

The only key not proven this way was “A6 to B15” this pair aborted the setup and took me to the command prompt. I suspected this was “F4” which is the key marked to quite the setup routine.

Later I tested this using a keyboard test site I found and it was indeed the pair for F4. Had I located the keyboard test program sooner I may have used that to test the rest of the key presses. The one I found though gave rather less information then the “Retropie setup routine”. As it was not able to distinguish between “Left Alt” and “Right Alt” etc.

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USB Encoders

Dell USB Keyboard Encoder

Home Brew

While looking for encoder options I was surprised to find quite a few options ranging from some cheap Zero delay UBS encoders to the Ipac 2 and Ipac 4 as well as a hat that sits on a Pi 3b+.

I also found some made from old USB Keyboards. I am not sure if using one board per player is the way to go with these. Which is what you would do with the Zero delay USB encoders.

I had a spare old USB encoder and so rather then buy parts I have decided to use that. I kind of like the idea of putting a old keyboard top use idea.

Having removed the PCB from the old keyboard, I then sanded away the black conductive coating on the pads and then tinned them with solder.

Next I tinned the ribbon cables and soldered them on place. I could have just identified the connections I need and only soldered wires for them. However, I am going to take all of them to a strip board and then put a terminal or a socket on for each wire.

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Joysticks and Buttons

My order for joysticks and arcade buttons arrived today. I note that I did not remember to order the optional white switches. Instead I seem to have ordered 2 more Yellow

Parts Order:

Sanwa JLF-TP-8YT Ball Top Joystick

Sanwa JLF-TP-8YT Ball Top Joystick (Black)

Suzo Happ Standard Concave Arcade Button (8 x Yellow)

Suzo Happ Standard Concave Arcade Button (6 x Black)

Suzo Happ Standard Concave Arcade Button (2 x Red)

Suzo Happ Standard Concave Arcade Button (2 x Green)

Sanwa JLF Joysticks and Suzo Happ Buttons
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Knock’d Off

After a lot of thinking and a chat with my better half I have decided on the colour scheme for a two player arcade machine.

Her late father and her brother both raced banger cars under the historical family name of Knock. They formed part of a team called Knockspeed. She like them has also raced banger cars, but not in the team colours of Yellow and Black. She raced as the “The Mummy”!

The Mummy

The Red and Green buttons will be for Coin and Player Selector. We chose these rather then the ones with Coin and Single and Double Player Motifs on them. The main reason was to keep a car based theme the colours of traffic lights stop (Red) and Go (Green). The white buttons in my layout above are a option for side mounting on the arcade case. These would be handy when playing video pinball type games.

I am most likely not going to be buying the artwork for a “bitcade” or similar cabinet. Although I might buy a blank wood kit as I have limited space and tools to make a cabinet from sheet ply wood or MDF boards.

Having quickly decided to make the colours yellow and black as a nod to my father-in-laws memory. I have figured on the games machines header display also carrying a nod to the family name of knock.

My machine is going to be called “Knock’d Off”.

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Heat Syncs for Pi

Seeing as I will be running the Pi 3b+ as a arcade machine, I figured it might be a good idea to add a small heat syncs. I did consider buying a heat sync case for it. They look great but this pi will be eventually hidden on a cabinet.

I did in fact order a case of this type then swiftly cancelled the order as I concluded that with the scarce availability of the “ipac 2” usb encoder “as used in my friends arcade machine”, I may end up using a Pi hat usb encoder. If that proves to be the way forward then such a case would not fit. Therefore I am holding off ordering a case until I have decided on my way forward.

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