This is a Yamaha XG card, the SW60XG to be exact. It’s an audio card for a PC which extends the MIDI standard to include over six hundred instruments. By today’s standards the almost twenty year old card isn’t all that powerful, but it is interesting to see it used as a standalone device.
[Benji Kimba] posted the video overview of his project which you can watch after the break. The image above is found at about 2:35 seconds and about twenty seconds later you get a look at how he patched into the conductors on the edge connector on both sides followed by the MIDI in and out connections. Finally, we get a look at a proper schematic at the four minute mark which details the pull-up resistors, hardware reset circuit, and the optoisolator he added for the MIDI connections themselves.
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Here’s a really fascinating circuit that implements a combination lock using relays and logic gates. Even with the schematic and written explanation of how it works we’re still left somewhat in the dark. We’ll either pull out some paper and do it by hand this weekend, or build it chunk by chunk in a simulator like Atanua. Either way, the project sparked our interest enough that we want to get elbow deep into its inner workings.
From the description we know that it uses a combination of CD4017, CD4030, CD4072, and CD4081 chips. You’re probably familiar with the 4017 which is a decade counter popular in a lot of project. The other chips provide XOR, OR, and AND gates respectively. The relays were chosen for two purposes. One of them activates when a correct combination has been entered, effectively serving as the output for the combo lock. The other two are for activating the clock and affecting a reset if the wrong combination is entered.
It makes us wonder if this would be incredibly simple to brute force the combination by listening for sound of the reset relay activating? It’s hard to tell from the video after the break if you can discern a wrong digit from a right once just based on sound.
Continue reading “Combo lock uses relays and logic gates”
Charlieplexing is a technique that allows you to drive a larger number of LEDs than wouldn’t be possible with the same number of I/O pins on a traditional multiplexed matrix. If we lost you there just think of it as lots of blinky lights connected to a small number of pins. It works by leveraging the one-way nature of a diode. Current will only flow through an LED in one direction so if you hook up your display in a clever way you can drive multiple LEDs from one I/O by switching the polarity of that pin between voltage and ground. [M.Rule] recently looked at using Charlieplexing with LED modules. His conceptual approach to the problem is different from those we remember seeing before and it’s worth a look.
Instead of just using the formula to calculate how many LEDs he can drive [M.Rule] is using a table of I/O pins to establish how many and in what order these displays can be connected. Each colored set of blocks represents an LED module. The graphic above shows how 18-pin can be utilized. He even filled in the unused pin combinations with input buttons.