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.
That doesn’t actually mean it’s OK, there are cases where transistors and other descrete components are “semi-burnt” (tests check out, yet it doesn’t work or doesn’t work as it should). The ”not so reliable" test would be to use a multimeter and see the voltage drop between B-E and B-C. The definitive test would be to make an actual amplifier circut, use the transistor in it and see if it works and if it distorts the sound (there are also cases where the PN substrates are somewhat depleted or damaged, either through use or a manufacturing error, so it works, but distorts the signal).
Do the light test, see if that passes, then do the multimeter test, see if that passes as well. If they both check out, 99% chance the transistor is OK. That 1% can be eliminated with the test circuit amp test.
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.
Hm… don’t know why that happens, never made a particle detector, but I have modded TO-3 cased transistors to be photodectors, they usually worked great.
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.
If I was to guess I’d say the purpose is to establish familiarity… assuming this community migrated during the great reddit migration… also i think it looks cool so…
You want hysteresis and an energy gap - which means putting energy into the system. You could use a latching relay to minimise insertion loss, however the loss in a conducting MOSFET can be pretty minimal.
SLAs self-discharge, of course.
If the load versus time is predictable, you could use a latching relay and delay voltage checking until the time window for potential cut-off. Or make it entirely period based and not test at all.
It may be that you never need to sense voltage, if your time period between recharging is small enough.
Many operate on that basis - the time interval between recharging may be out of their control (in our case, once, we only had mains electricity between 2am and 4 am each day…) and they provide themselves with enough battery capacity to last that time interval, with a reserve. So no low voltage cut off necessary. So no testing necessary.
I once got inspired by this: scoollab.web.cern.ch/diy-particle-detectorIt uses photodiodes instead of BJTs. Advantage is that you can get some which are easy to decap. I did not get it to work :/ but also did not spend so much time. I think what is really important is to properly shield the circuit from electromagnetic radiation, use a battery (low-noise) and also shield the detector from light.
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.
Is the ground for the voltage rail and input signal the same?
Yep.
What exactly is wrong with the circuit I built? I want the LED to only turn on when 5V is supplied at the input, right now the LED can turn on if I connect the ground to the voltage rail supply even without an input voltage.
Schematic of exactly what you did… not what was on paper, how it is on the breadboard.
I’ve seen the post on Adafruit with the feedback resistors connected to the same ground as the rail supply, but the circuit diagram does not show where the input voltage ground is? Link: blog.adafruit.com/…/ask-an-educator-making-a-non-…
Use a single power suppy (GND and +12V) and tie the Arduino’s GND with that GND.
Your circuit fails because the Arduino’s GND is tied to the -12V from the dual power supply, so the +5V that the Arduino outputs equal to -7V on the non-inverting input. Since this is a non-invering schematic, the opamp doesn’t invert the signal. Instead, it tries to double the -7V to get -14 on the Out, but since you’re powering the opamp with -12V, it can’t achieve a voltage that low, so it outputs the maximum it can give: -12V.
The LED turning on even when there’s no signal on the non-inverting input is probably a floating input problem. It picks up EMI so it just amplifies that. Try connecting the non-inverting input to GND, the LED should turn off… that or you burnt one of the opamps, lol, try the other one in the package.
I tied the Arduino’s GND to the power supply GND, the output is still 10V, tried different ICs as well, not really sure what the issue is at this point. Tying the non inverting input pin to ground does turn OFF the LED, but the led stays on regardless if the 5V is coming from the arduino or not, it seems that the op amp outputs 10V regardless of the non-inverting pin, however if I use different resistors to lower the gain or change the input voltage to 3.3V instead of 5V, I do get the output voltage. I just don’t understand how there can be 10V at the output with no voltage from the inverting or non-inverting pin.
Well, you should get 10V. You input 5V, the voltage gain is 2, so the output should be 10V. I don’t see a problem here, the circuit is working as expected.
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.
the first thing i'd do is connect the GND from your arduino and from your power supply. At the moment there does not seem to be a common ground or it is off picture.
The circuit works when there is a common ground (makes sense ofc but originally I thought they had to be separate), I didn’t want to put 5V and 12V on the same rail of the breadboard. Now what I find strange is that even without the 5V input voltage, I still get 10V at the output of the Op-amp which is very confusing.
Just a word of caution - education is a process of diminishing deception. Books provide a simplified version of real World electronics. Universities and colleges put a lot of effort into designing lab practicals that will actually work and give the predictable results that students expect.
So the normal learning process when it comes to op amps - is to read and understand the theory. Then complete those crafted lab practical exercises - having been introduced to the added complication of systemic and random errors. Then do your own thing, when all the remaining Real Life complications hit you like a brick.
So, if you can find a course in analogue electronics, even a distance learning one, you might find the steps are smaller and more easy to assimilate.
I understand your caution, however I understand the theory behind OP-Amps, theory can only go so far which is why I’m building a circuit on a breadboard now. I should clarify that the basic rules for ideal op-amps I have a grasp of, although I can never seem to remember these rules. For example, I have the formulas for a BJT and MOSFET transistors memorized because I spent a lot of time reading and using them in practical applications. Op-amps I have spent a lot of time reading but no time building circuits, which is essentially what I am trying to do now. I have a degree in EE, and at this point this is one of the basic components that wasn’t covered much in university, nor did reading or doing practice problems help. I’m very much a hands on learner, I can read formulas and equations all day but if I don’t apply what I learned I’ll forget it after several days unless I repeatedly practice.
What worked for me, that may not do so for anyone else - is to take an existing circuit (usually a reference one provided by a manufacturer) and build that. Get that working (sometimes, it hasn’t worked- the manufacturer’s technical support department has often been very helpful, especially when their reference design has a design fault or has been misprinted - after doing that, they used to send me unmarked, pre-production chips/etc to play with and provide feedback).
Then modified that design, to test my understanding. Tried different board layouts, guard rings, etc and documented the effect. When it didn’t work as expected - took that back to their tech support to see if we could work out why.
So, for me, taking something that works and keep modifying it, just a little.
Usual situation - if I needed to interface to 5 cameras I wouldn’t start with ones that needed: “The DVP physical interface consists of a single, 100-conductor, 110-ohm cable organized. as 45 differential signal pairs. These signal pairs consist of the following: • 36 RGB data pairs. • 2 clock pairs.” So, you would be interfacing to 5 x 45 differential pairs. I’d be looking for camera modules with serial output…
Or, as you suggest, give each camera something that can convert that lot into a single serial data stream. Or even process it down to a QR code and just send that. Or even do what-ever it is that you want to do with that code, once received.
Connecting each camera to its own ESP32, which process the data and sends only necessary information to the main ESP32, I think is a cool idea.
I plan to use this Schamatic as a guide for building the ESP32 cam parts on my pcb, although I’m sure I’ll be using a slightly newer ESP32: github.com/SeeedDocument/…/ESP32_CAM_V1.6.pdf
It seems that the PINS U0TXD and U0RXD are free. Can I use these to connect them to the main ESP32 via UART or is there a better way to connect all ESP32 cams to the main ESP32?
And there is one more question. How can I program the ESP32 of the cams? The main ESP32 will be connected to a Micro-B SMD USB connector. Do I need another one for each ESP32 (for the cams) or is it possible to program all ESP32 via the same USB connector?
Depends on your programming abilities. You can set up a “1-Wire” bus and put the lot on that. You could have one microcontroller as master and the rest as slaves - your external USB connection would go to the master and it could, in theory at least, then pass on program upgrades to the others. Clearly they would all have to be programmed individually, originally. But, quite frankly, the investment in time and effort on setting all that up? If you had dozens, hundreds - then yes. But you only have a small hand full. I’d just bring out their USB connections and program them individually, via those. I think each one has a unique identifier, stored in ROM - so they could all run the same software and include that identifier in messages on the bus.
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.
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