Well, arguably keeping the resistor the same value would result in a somewhat known state, and changing it would put it in an unknown state. The unknown state could be better or worse. I can't see enough to know what the circuit does to say.
What you could do instead, is set the resistor to the same value, but rated for higher thermal dissipation. Then measure how hot it gets to identify if the real problem is somewhere else. Another part might burn/explode instead though, so I'd consider carefully how to proceed, and probably wear goggles + have a fire extinguisher in the room.
My main concern is by 'fixing' it with a resistor with higher thermal dissipation, I've created a fire hazard because that dissipated heat now has to 'go somewhere', which may be the plastic case. A thermal camera is handy to see if some part of the board gets unacceptably hot during normal operation.
It looks like 1GΩ (black-brown-white gold). But that doesn't sound likely unless you have a very high voltage bread maker.
If we treat the black band as discolored-brown, and read it the other way, we get (yellow - white - brown - brown) which is 490Ω and closer to your measured value. I wouldn't rule out (yellow - white red - brown) either at 4.9 kΩ, although that doesn't match closely to your measurement.
A good question is 'why did the resistor burn?'. If I didn't know why, then I would assume that replacing it will just result in it burning again, although maybe not immediately.
...but how in the world do you burn a 1 GΩ resistor? That looks sort of like it could be a 1 watt resistor too. So back-of-the-napkin this would have to be from over a 30kV supply. So that sounds a bit off.
Unless it isn't. One hell of a bread maker then. I want one.
Well, for #2, there are excellent modules based on the TP4056 that cost 1$. They charge lithium-ion batteries only. So check the label (yes, I know it clearly says Li-ion but don't trust strangers on the internet for safety facing stuff...), if it says Li-ion, then these are great.
For #1, probably one of those fat traces in the flexible cable is BAT+ and the other is BAT-. I would look for a way to safely remove the plastic coating in such a way that I can't accidentally short circuit it. For example, exposing the copper for BAT+ on one side, and BAT- on the other.
I suspect the reason it's not working, is something I don't currently have the tools to measure.
With an OK reflected light microscope I could work out whether there's a glass or clear epoxy coating on the silicon. With an alpha spectroscope, I could characterize the source better. Tools are cheap in Asia, but the space to put them costs a fortune...
So I'm going to shelve this for now and maybe try to build a BJT amplifier for a PIN photodiode detector. I've etched some boards. Fingers crossed.
the smart thing of course would be to buy a scintillator crystal, but I hate the inelegance of it. It shouldn't be necessary.
I suppose you could use a bus or something to cycle through the cameras one at a time?
Why not use a lower-resolution I2C camera module? I2C allows multiple devices to be connected to the same I2C port, as long as they have different addresses. You can also use one with lower resolution for QR I suspect.
An alternate method would be to buy QR-code recognition modules, with some form of serial output. Then connect all of those to the ESP32, if you can do 5 software serial ports. More expensive this way though.
No, it's not possible to do it without current draw. You can do it with really, really low current draw though.
Ignoring MOSFET stages for the moment, I could design a system that could do this, with a power consumption of under 0.1 uA when in the low-voltage cutoff state.
I'd use a TPL5110 and an Attiny10 to do that.
Alternatively, if ~50 uA is OK (it really should be), then I'd just use the Attiny10 on watchdog timer, and save the cost of the TPL5110.
If I absolutely did not want to use the SLA to power that system (as an academic exercise), I'd use a separate CR2032 coin cell. That ought to last 3-5 years. Or if there's ambient light, a calculator solar cell and a supercapacitor would make it self-powered. I could design a system that could last overnight on just a few hours of ambient light during the day. Modern microcontrollers are a marvel!
The amount of power drawn by a reasonably designed system should be many orders of magnitude less than the self-discharge of the battery. So not worth worrying about unless it's very poorly designed for some reason.
Wow, OK. It failed pretty hard. Fail on the light test, and failed to switch with the base saturated. Also measures a resistance close to zero between all pins.
I'm actually quite surprised! The potting compound 'surgery' went very smoothly, like peeling off a sticker. Well, these things happen when abusing semiconductors I guess. I've got spares, so no big deal. If it fails again, I'll go find an alternative BJT that does not have potting compound.
I've gotten a similar circuit to work. Good shielding on the preamp was indeed key.
That was like 12 years ago though. Back then I used a battery. I probably know enough to get it working with a switched power supply now, which would be way more convenient.
The PIN diodes aren't cheap though! Also some are export controlled. Not the one from that project though. I have a few around that I'll use if I can't get this to work.
The BJT method is attractive due to really low cost. I never managed to get it working though. There are enough independent reports of the method working online that I think it's possible, but the documentation hasn't been sufficient to easily replicate it.
It might be something boring like some manufacturers put a clear coating (e.g. glass) on the internals of a type of transistor, and others don't.
Maybe -- easy to check, at least. I'll just shine a light on it :)
The coating came off pretty easily though. The bonding wires pass visual and mechanical inspection, and do not short on the case or other parts of the transistor.
However there's a weird little caveat -- some papers attribute the piezoelectric effect to organic collagen fibers. Others attribute it to the inorganic component (apatite). In the end this paper seemed to have a reasonable measurement process so I've just ignored the exact cause of the piezoelectricity for the moment. From their tests, orientation of the bone is highly important.
They use an applied voltage of 100V then amplify (100db). I'm reasonably competent working with moderate voltages, but would prefer to try something under 30v as a matter of convenience (e.g. what I can reach with a DC-DC boost converter).
Normally though, I just hook up a crystal oscillator to a hex inverter @5V or to an MCU with some caps. I'm not entirely sure how I'd build an equivalent circuit at 30V! Doing unnatural things with crystal oscillators hasn't really come up much in my studies or career.
I tried with cooked bone, that tends to be what I have more of lying around :D
I don't recall the voltage I tried, but it was probably something in the range of 5-9v. I didn't try with a very thin slice, it was a few mm thick. Probably a thinner slice is the thing to try. That's a bit hard with bird bones (hollow), so maybe I'll have to cook something else. I don't have a microtome, so I'll have to cut some thin slices by trial and error.
I would hazard a bet that orientation matters. The studies that measured bone piezoelectricity seemed to suggest some orientations made more sense than others, but I don't recall what exactly. In any case, they had... very different applications in mind.