Archive for February, 2011

Hammond XB-2 ROMs?

Saturday, February 12th, 2011

I have two secondhand Hammond XB-2 Hammond clones (c’mon, even if it had made by Hammond proper before being bought by Suzuki, a solid-state, digital audio synthesis keyboard is still a clone) which both appear to have bit rot in their firmware EPROMs, apparently a common problem with these keyboards.

I’d be extremely grateful for pointers to where I could get new EPROMs or download images to burn myself, or to another XB-2 owner willing to read out their EPROMs to assist. Heck, I’ll burn you another copy so you have a fresher set when yours bit-rot.

They’re IC16 and IC17 and they’re 27256es.

Monitoring Battery Voltage

Saturday, February 12th, 2011

Battery and voltage regulator schematic

Hey, real EE types out there, is there any reason I can’t monitor 12V battery voltage using a simple voltage divider into an A/D input of a microcontroller that’s powered by a voltage regulator on that same battery?

This seems straightforward, but I ask because there seem to be a lot of fancy circuits and devices out there for monitoring supply voltage. It seems to me they all revolve around monitoring the device’s own VCC and where to get a reliable AREF when you don’t trust your own supply.

In the case of monitoring a battery voltage that will always be much higher than the dropout of the voltage regulator powering the microcontroller which generates its own AREF, I can’t think of any reason to get fancier than this.

I would Just Do It but I don’t have a good test setup for this and I’m getting ready to commit it to a board layout.

Water and Electronics

Friday, February 11th, 2011

Three days after we upgrade an ancient switch in the campus golf course headquarters, a supply pipe breaks overhead and pours water into our new switch. It’s “environmentally hardened,” but that doesn’t seem to cover immersion.

As a state university, we’re self-insured and there’s no way we’re getting a T&M refurb from the vendor on water damage, no matter how generous they may be. So I’m getting nothing for this dead switch and I may as well see whether there’s any hope of cleaning it.

Cisco 2940 switch interior after water damage

Oh. Nope, not really.


Temperature Deviation Alarm Board for PID Crockpot Controller

Friday, February 11th, 2011

After assembling my PID crockpot controller, I successfully cooked a couple of medium KC strips at 60°C. When I tried to cook medium-rare at 55°C, though, I kept finding the temperature at 59°C. Not believing that I’m destined to eat medium steaks for the rest of my life, I want to fix this.

My first guess about what’s happening is that the crockpot is well-enough insulated that the controller’s longest delay for how often it turns on the heat is still too short. If so, I may get better control using the crockpot on its (dumb) low heat setting, which could be activated more frequently without driving the temperature as high.

PID crockpot controller with temperature deviation alarm LEDs

Regardless, if I can’t trust the controller to control, I need a monitor external to the controller to let me know when the temperature has gone out of range so I know I don’t yet have a satisfactory system. Although the immediate problem was overheating, I should also like to know about undertemperature problems as well. Happily, the controller has temperature deviation alarms; but less happily, they are momentary and only show when the temperature is currently out of range. Enter the alarm latch.