• Time to ditch the 2764s

    11/08/2024 at 06:25 • 0 comments

    © Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons), Mitsubishi M5L2764K-5377 , CC BY-SA 4.0

    After creating a minor tweak to the firmware for #8042 clock (the PCB version, the breadboard version was disassembled years ago) I needed to burn some 2764 EPROMs with my trusty TL866A. Unfortunately some of the EPROMs couldn't be programmed, but others could. The common factor seemed to be the need for 21V Vpp. Usually the C (for CMOS) chips could be programmed.

    I had been able to program these in the past so either my TL866A had developed a fault or the open source minipro software for Linux had a bug. I couldn't find any reports about this in the repo, so that would point to the former. Or hardly anybody programs 21V Vpp EPROMs any more so never hit a bug.

    I had already written about ancient 2[57]{16,32} EPROMs that require 25V Vpp, and had concluded that I would not be able to use them. So for these 21V Vpp 2764s, I think the most expedient way forward for a lazy cat is not spend time working out whether my programmer or the minipro software is at fault, or even trying the Windows minipro software in a VM, but just bin these chips. (Or if anybody wants them for the cost of postage, PM me.)

    Fortunately my designs already cater for using 27C128 or even 27C256 EPROMs in the same 28-pin socket, and I still have a lot of those, probably more than I'll ever be able to use up, as I'm more ancient than the chips. And anyway the non-CMOS versions of the 2764 are more power-hungry.

  • Assembling a 120 W bench power supply

    10/20/2024 at 19:38 • 0 comments

    I ordered a XY-SK120 buck-boost converter with digital controller with LCD screen from Aliexpress. With it I can dial up any desired voltage and use current limiting to forestall damage when first powering up projects. It has many other features. From the specs it's quite an impressive piece of electronics for its small size. Input can be 6-36 VDC and output 0-36 VDC at up to 6 A and it handles up to 120W.

    I chose the cased version. It's more than just the bare converter board with banana sockets in an enclosure. At the back is a cooling fan and a power input panel that takes various sources, including terminal block, barrel socket, some kind of Molex socket, and even USB-3 PD input. A cursory inspection shows that diodes isolate the inputs from each other. These extras account for the higher price.

    The fly in the ointment is poor documentation. It would be nice to know how to operate the UI without trial and error. Not even a slip of paper in the box. But a bit of hunting found an instruction manual online. From the modification date, less than 3 months ago, the firmware is still being improved, and in the future it might be possible to update it using the serial interface.

    Normally one would use a SMPS or an old laptop power brick for the input. I decided to put to use an old school power supply board possibly from an LA30 Decwriter that the board for #Flashing LEDs from old printer electronics came from. In the board pictured below, only one set of bridge rectifiers and one large capacitor are in use. There are actually two independent power supplies on the board. The low voltage one supplies digital logic via a 5 V regulator, one of the large TO-3 cases. I won't be using that half. The high voltage one supplies the electromechanics. The capacitor is a whopping 10000 µF rated for 50 V so lots of margin. Nominal voltage level was probably around 30 V. A 24 VAC appliance transformer that I was given feeds the board.

    For the enclosure I used an old Ryobi timer saved from e-waste. It seems to have been an appendage to unknown industrial equipment. The inside was gutted to fit the PS PCB.

    That such a small controller can provide 6 A is a testament to how much the power density of electronics has increased over the years. (But some reviews mention that the cooling fan may be inadequate at high power levels.) The current is more than the old bulky linear power supply can supply. The fuse on the rectifier board is rated at 2.5 A. The transformer is rated at 1.5 A. (Although at lower output voltage, more current can be supplied, as the converter is switching mode.) Anyway this is enough for my needs for the near future.

    Oops, I forgot to order 4 mm banana plug cables. Next round then. Can't buy everything in the shops all at once. 😉

    Well that takes another tuit off my round tuit list.

  • Simple opamp tester

    09/26/2024 at 11:07 • 0 comments

    I have many 8-pin opamp ICs such as the venerable 741 in my junk box, some pulls, some from grab bag purchases. I wondered how many of them are working. So I put together a simple circuit to check basic opamp function. I assembled it on perfboard as it's a simple circuit and I only need one.

    It's a familiar relaxation oscillator. Normally we need balanced voltage rails for an opamp, but the resistor network R1, R2, and R3 establish upper and lower bounds of roughly ⅓ and ⅔ the supply voltage. The values chosen make the LED to blink at about 3 Hz. The pin numbers are for the 741 and others with the same pinout. It's just a go-nogo check and doesn't test advanced characteristics. The tester found a handful of duds which I can now throw out. So if nothing else, I know that I have lots of blinky ICs in my collection. 😉