Curse of the green crocodile clips
Well, I've made a smidgeon of progress on the persistence-of-vision LED array gadget. It needs to be battery powered, so that I can put it in my pocket and use it without a mains supply. That means four AA batteries (6V or so) and a low-dropout regulator. I happen to have a lot of LM2941 regulators, and they're suitable. So, build one up to check the resistor values (it's an adjustable reg) and make sure it works. Seems OK on a PSU, and having found four good batteries, it's OK on those too. Testing it on the real circuit was a bit flaky; sometimes it worked, sometime it didn't. Drat.
Turned out that the voltage at the load was about half a volt too low, but the regulator output was fine. I was losing half a volt across a green crocodile clip lead. They do sometimes fail, so I took it out and got another one. Still not right. Sure enough, the second green crocodile clip lead was also faulty! A white one fixed it, and the LEDs came on at full brightness and everything worked.
The circuit draws about 160mA from the AA batteries, so I'd better have some spares handy...
Turned out that the voltage at the load was about half a volt too low, but the regulator output was fine. I was losing half a volt across a green crocodile clip lead. They do sometimes fail, so I took it out and got another one. Still not right. Sure enough, the second green crocodile clip lead was also faulty! A white one fixed it, and the LEDs came on at full brightness and everything worked.
The circuit draws about 160mA from the AA batteries, so I'd better have some spares handy...