4The gap between my last post and now has been filled with sporadic bursts of activity curbed mostly by the amount of time that can reasonably be spent on projects and whether I’m in the right frame of mind to focus on something that requires a degree of patience and accuracy. All that aside the intervening time has been spent on three particular projects.
1) Arcade machine.
I’ve wanted to build one of these for a while and with the I3 finished and most of the parts already collected it seemed like an ideal opportunity to tackle this one once and for all. A flurry of jigsawing, gluing, screwing, bogging and sanding quickly turned this
For anyone interested the plans can be found for free here.
At the moment the base of the table is pretty much finished, all that is needed wood wise is the table top and the braces for the control panels. The top of the cabinet only needs a quarter sheet of 25mm thick plywood but no one seems to sell sheets that small and the people who assure you vehemently that they regularly have offcuts of that size in that thickness never seem to … If anyone knows a good source for less than full sheets or somewhere with a price so good that I could buy a full sheet then I’d be greatly appreciative.
On the control panel front the diagram for the plans was sent off (and then sent off again because everyone bar one source seem to be too lazy to convert 3 measurements from imperial to metric) to 6 places that do sheet metal fabrication so I could get a couple of blanks knocked up. Eventually the quotes started trickling back with prices ranging from $48 for two to a whopping $160 +GST. In the end I settled on the supplier that could be bothered tacking the imperial conversions (even though I later sent them the plans in metric). They responded quickly, had a good price and did a good job. Thanks Classic Sheet Metals in Henderson.
These blanks were then drilled to a template cobbled together from various other arcade panels and the buttons and joystick were then test fitted
and given several coats of satin black spray paint before the buttons and joystick were refitted
Turns out that two player machines need two coin slots. Guess that makes sense. This caused a problem as the coin slot thingy that I had only had one slot and the supplier no longer sold identical units. Average.
Anyway coins are on the way out, contactless payments are where it’s at so introducing ARCredit.
Arduino Nano with RC522 RFID reader and the obligatory JY-MCU Bluetooth Module.
This particular reader was chosen due to its low-cost and eBay availability, this came at the cost of having a less than ideal method of communication with the MCU namely SPI. The even more annoying this is that the IC that the reader is based around also has a serial connection, it’s just not broken out. Instead then of issuing simple strings out a software serial port I had to resort to using a specific library created to communicate with this reader, but unfortunately at some point written in Italian? with not much basic documentation. After spending a couple of days trawling through the code and trying different things I managed to get the code working well enough for my specific application and another couple of days of fiddling around had the turd fully coated in glitter.
Basically the reader works with the Mifare chips which you can get in token or card form. Using a custom access key the reader pulls the factory serial number and a 16 byte string from two different places on the chip and makes sure that they both match the strings written into the code. A third location is read with a single byte retrieved which represents the number of “credits” remaining on the token. In practice a player would hold down their “coin insert” button on the arcade machine and swipe their tag. The Arduino would check that the tag is valid and then trigger an output pin to send the coin insert signal to the arcade emulator. Each successive swipe deducts one coins worth of credit from the tag and then triggers another coin insert signal. The software has a customizable pricing structure in which you can define the number of credits that are taken off any particular tag each time the token is swiped.
The Bluetooth module is there for the purpose of adding credit to the tags. Connect a cellphone running the ARCredit software and send the appropriate string to the Arduino. The next tag that is swiped will then have its balance set to the value sent from the cellphone.
Once the rest of the arcade machine is finished the reader module will be mounted to the a perspex window in the side of the cabinet with the Arduino and Bluetooth mounted properly on a PCB elsewhere inside. As usual the code is up on Github, any misuse and token fraud will be met with severe repercussions.
3) Battery Charger
I think I’ve mentioned before that the battery charger in the Shopping Trolley is a little suspect. I’m sure that F&P make some good stuff and that the original charger is perfectly good for the stock batteries but ever since I put the new double capacity batteries in the charging light has always been on and the battery level indicator has been a bit suspect. The last thing that I want to do is over discharge the batteries and shorten their life
To remedy this and protect the investment made in the batteries I decided to fiddle around with the charging system, specifically setting it up to better balance and maintain the batteries when the trolley isn’t being used.
As a result 6 massive-key-switches-of-doom have been added to the foot well. Switching the three on the right connect the batteries in series to the rest of the system for riding around where is switching the three on the left connect them in parallel for charging.
The string is there to make sure that only one side can be switched on at once and even though the switches each came with one key (making 6 in total) three have been destroyed in the fires of Mt Doom (hidden away where ill never be able to find them). This combined with a healthy dose of “NEVER EVER DO THIS [AGAIN]” to any potential operators should prevent potential 12v deep cycle battery short-circuit fun.