Hi -
I have a puzzle for which I can only come up with one solution - and I'd like to know if it makes any sense!
I have built some units for a friend based on PIC18F2321 micros. The actual function is not relevant, but they are designed to operate outside, overnight, and to control some high-powered LEDs. The software includes a test of the battery voltage at switch-on in order to confirm that there is sufficient charge to run the units all night. Another function is that, when the units switch off the LEDs, at dawn, before doing so they read the battery voltage again and store it in EEPROM. This helps to check when rechargeable batteries are getting past their useful lives.
Last night I put two of these units out. When I went to bed, they were operating perfectly, having switched on automatically at dusk. When I checked them this morning, BOTH units were flashing 'b' on their displays. Now, the only part of the software that allows this to happen is the initial battery check, which displays a flashing 'b' to indicate that the battery voltage is inadequate to last through the night. Furthermore, the battery voltage had not been saved in EEPROM (don't ask how I know, just trust me!)
The only explanation that I can give for this set of circumstances in the units is that, shortly before dawn, when the batteries were fairly well-used, the units had been reset, before the auto-switch-off and saving to EEPROM function occurred. Having restarted, the self-test had then determined (correctly) that the battery voltage was insufficient for another night's use and displayed the warning signal.
But these two units were sited about 50 metres apart, in open countryside. So the only explanation that I can offer for this is that some form of electrical disturbance had reset both units before dawn. And the only kind of electrical disturbance that I can envisage out here (in a very rural area) would be lightning.
I was not aware of any kind of thunderstorm, but it is not unknown for us to have electrical storms in this area, with lightning, but without (audible) thunder and without rain.
Can anybody else think of a reasonable explanation for this, or does my explanation make sense?
Phil
I have a puzzle for which I can only come up with one solution - and I'd like to know if it makes any sense!
I have built some units for a friend based on PIC18F2321 micros. The actual function is not relevant, but they are designed to operate outside, overnight, and to control some high-powered LEDs. The software includes a test of the battery voltage at switch-on in order to confirm that there is sufficient charge to run the units all night. Another function is that, when the units switch off the LEDs, at dawn, before doing so they read the battery voltage again and store it in EEPROM. This helps to check when rechargeable batteries are getting past their useful lives.
Last night I put two of these units out. When I went to bed, they were operating perfectly, having switched on automatically at dusk. When I checked them this morning, BOTH units were flashing 'b' on their displays. Now, the only part of the software that allows this to happen is the initial battery check, which displays a flashing 'b' to indicate that the battery voltage is inadequate to last through the night. Furthermore, the battery voltage had not been saved in EEPROM (don't ask how I know, just trust me!)
The only explanation that I can give for this set of circumstances in the units is that, shortly before dawn, when the batteries were fairly well-used, the units had been reset, before the auto-switch-off and saving to EEPROM function occurred. Having restarted, the self-test had then determined (correctly) that the battery voltage was insufficient for another night's use and displayed the warning signal.
But these two units were sited about 50 metres apart, in open countryside. So the only explanation that I can offer for this is that some form of electrical disturbance had reset both units before dawn. And the only kind of electrical disturbance that I can envisage out here (in a very rural area) would be lightning.
I was not aware of any kind of thunderstorm, but it is not unknown for us to have electrical storms in this area, with lightning, but without (audible) thunder and without rain.
Can anybody else think of a reasonable explanation for this, or does my explanation make sense?
Phil