Maybe you can use this to find more connectors that could match yours: connectorbook.com/identification.html?m=NT&n=lo_p…It has a pretty handy identification tool (you can even browse by pictures). It usually suggests quite an amount of connectors but it can guide you in the right direction and you can look at the according datasheets to find out more. By the way the creator of this community made that homepage and a book related to it (or probably the other way round 😅).
https://sensepeek.com/ do manufactur those nice PCBite SP10 probes. New improved series: SQ10 probes. They also have 500MHz Oscilloscope probes! They are awesome :D
The SensePeek PCBite system is really nice. They're the best board holders I've ever used, very stable. Great for testing, and great for soldering. The probes are ridiculously helpful, it's downright easy to probe adjacent pins on a 0.5mm pitch QFP (with some magnification)! All rather expensive, but very, very worth it for the time saved.
The Internet corollary to Murphy's Law: If you post something, it's public forever unless you need it later, then it'll have link-rotted. Anything you want to delete will be archived, anything you want to save will be deleted.
For this application you should be using a bench power supply with current limiting, not a "serial bulb" (I assume you mean a fuse, which is designed to break at a low current, however these are most typically rated for several amps, not typically in the mA range). You can set the voltage and a current limit. If the current goes beyond the limit, then the power supply will drop the voltage to keep the current below the limit or latch off. You can get a fairly cheap one for about $50-60 off of eBay, which won't be the best but is sufficient for hobby use
Hey, thanks for your reply. By serial bulb I mean a incandescent lamp in series with the circuit. I was looking for a cheap and diy option, but I'll take a look on a bench power supply. I still need to get me a decent one anyways.
Ah. It's not going to be possible to size it because the bulb is then acting as a resistor essentially. Unless you know what the equivalent resistance of the circuit you're testing is, and it draws a fixed current, you aren't going to be able to cap the current; Adding a resistor (or bulb) is just going to drop the input voltage and you will probably end up having other issues
It has the high current because it's cold, it only needs a short time to heat up and light up and the majority of circuits can handle very short overcurrent really well because the connections need to heat up before they break. Using a lightbulb for current limiting works pretty well.
output impedance of the signal generator you use to generate the square wave. When you set it to low, output impedance of the signal generator builds a voltage divider together with the internal pull up, and the device ends up sensing a higher voltage than "low". This is something you can see if you have an oscilloscope, try to hook up a probe to the input and ensure whether you get what you set in the signal generator.
some signal sources have no or limited capacity to drain current. And when you set it to low, this is exactly what it us supposed to do, drain current from the internal pullup.
As you mentioned in another comment, solution is a simple buffer. This could be an opamp, but even a simple nmos transistor should suffice (open drain as you said). But you need yo be careful with current ratings of the transistor, which you can easily calculate by dividing 5V by the pull up resistor. Send a message if you need help.
Before these, I suggest you yo use an oscilloscope or multimeter to measure the voltage when it is supposed to be low, and see that in fact the problem is that voltage at the input doesn't go "low".
I measured the signal generator alone, not connected to the input. It goes to 4.5V high and 0.001V low. Then I connected it to the input and measured at the input. I got 4.5V high and 1.1V low.
Also I ordered the 74LVC1G07 buffer along with a breakout board which should allow me to hook it up inline and test. I'll report back when I do.
It should do the trick I think. If you are working on electronics a lot, you may consider buying a breadboard and variety of resistors, capacitors and nmos, pros, bjt transistors in bulk for quick fixes instead of waiting for orders to proceed. Have fun
Interesting, I've never thought of doing it exactly this way. Usually I see high surface area PIN junctions used to detect particle impact either by reverse biasing the junction or by directly measuring induced voltage. The amplification stage is not so easy. This is for particle counting and energy measurement though.
What kind of radiation are you measuring? Gamma I guess?
I guess the first thing that comes to mind is that for a given signal, as Vgs increases perhaps the on-resistance at a given voltage does too? If so, it might be easy to measure the voltage drop across the MOSFET on resistance and how it changes with dose.
If I think of anything else though, I'll let you know!
Edit: I suppose you could also use an R/2R network to provide an increasing voltage to the MOSFET base, and measure the point where the output reaches some threshold, a direct measurement of Vgs. That should be pretty easy using one full output port of an Arduino and one of the ADCs.
Connect the gate to a function generator via a series resistor. (Gnd on the source pin) Drive it with a square wave 0v low 5+v high and observe the gate voltage on the oscilloscope. You will see a little plateau spot in the waveform, this is at the gate threshold voltage.
Using MOSFETs as TID sensors is common enough. A term that you can use for more research is RADFET. The best way to measure threshold voltage is to sweep the gate voltage. In my experience however, if you intend to measure this in a non-lab environment (say, in a satellite), I would recommend that you instead connect the gate to the drain, force a small constant current (maybe 10uA) from the drain to source, and measure Vds (which is equal to Vgs in this configuration). This won't give you the threshold voltage per se, but this will produce a voltage that changes as dose accumulates, is a far easier metric to measure, and is as equally valid as measuring the threshold voltage to determine TID. You can't really predict the shift in threshold voltage according to TID unless your MOSFETs are all from the same batch (manufacturing defects and tolerances), and you need to calibrate them in order to obtain a calibration curve (this is done by simply going to irradiate several (the more the better, I suggest at least 10 for statistical significance). Alternatively, you can buy pre-calibrated ones from companies who make MOSFETs for this intended purpose like Varadis. If you really want to measure the threshold voltage, you could read MIL-STD-750, which outlines how to measure the threshold voltage.
Hey I messaged them a bit, this is an undergraduate project with no budget (so a MOSFET tester is out of budget). I also suggested a sort of sweep method using an MCU and some op-amp glue, but I don't think they have sufficient background to get this kind of thing working yet (in fact I barely do, so probably it won't 'just work' with whatever I came up with off the top of my head).
What I was thinking is perhaps they can set Vds and Vgs to fixed values such that a particular MOSFET conducts a fixed current, e.g. 100mA, somewhere near-ish the start of the linear region. Then record the Vgs required to achieve this current for each of a set of MOSFETs, say a few dozen (because of part variation).
Then after exposing them to varying amounts of radiation (a few for each exposure level), put them back in the same test conditions and measure how the output current has changed, what Vgs will restore the same current, draw some graphs, discuss the advantages and disadvantages relative to the Vth method with regards to radiation dosimetry, conclude, and call it a day.
Think it would work? No need for an MCU or signals processing this way, so the science can get done with the tools they have.
Also I never had free access to strong radiations sources in undergrad, so am a little jealous. I barely got to use tritium, and that sparingly.
Hello, do i still need to apply a supply voltage of Vgs, or will only the current at the drain be the main source. Also, is this MOSFET sensitive enough for a cs-137 (661 keV).
Ultimately, yes you will need to bias the gate. If you put the MOSFET in the diode connection mode, the gate will automatically be biased when you force a constant Ids current. While I have never worked with this MOSFET nor with Cs137, I don’t see why it wouldn’t be sensitive. A few notes:
This MOSFET is in a TO-247 package, so make sure that you have the front of the MOSFET pointed towards the Cs137 source during irradiation, otherwise the leadframe will likely act as an attenuator, reducing the sensitivity.
This MOSFET is a HEXFET, which normally aren’t designed for continuous high DC power dissipation (they are meant for switching). So keeping the dissipated power in the FET would be best.
I’m not sure if there is a difference in general sensitivity between HEXFETs and other MOSFET types like VDMOS or traditional monolithic planar MOSFETs.
I’m not sure if you already planned this, put generally it is recommended for the MOSFET to have all pins grounded during irradiation. Biasing of the MOSFET can affect its sensitivity (depends on every MOSFET), so having all pins grounded keeps them in a constant state during irradiation (and lets all accumulated charge get shunted to ground, preventing ESD damage).
I’m not entirely sure, but I suspect that the die is mounted to the leadframe on the flat side of the package. In this case you should point the flat side towards the source.
I’m using lm334z as a current source, i’m still thinking and deciding on where to connect it to the MOSFET. Can you propose the wiring for the current source input once the MOSFET is in diode connection. Like for example, in a breadboard i used a wire to connect the drain and gate. then, i’ve applied a constant current at drain terminal with source connected to the negative. So to check the change in voltage, should i measure the voltage in Gate to source?
Hello, I have already tried to apply a microampere current (around 40 μA) using only Ohm’s law. I used a 2V input and a resistor in series. However, the LM334z is not working, and I am unsure of the reason for its failure. Will using an input voltage and a resistor in series work just fine?
I have also measured the Vgs, which reads at around 0.117 mV. What do you think about the measured Vgs? Technically, it should be around these values, right? Considering that there is a very small current.
You will probably need to increase your voltage. I haven’t ever used the LM334, but it will need a minimum voltage across it. I don’t know if you are still using the IRFP250N, but if so it has a threshold somewhere between 2V and 4V for 250uA, so the threshold won’t be as high but it should be close. I would try using 5V if it’s fine with your setup.
For the suitability of the resistor method, you should do the math on how a change in Vds will affect the current, and then calculate how much this variability in current will affect your readings. If this error/innacuracy is acceptable, then why not.
Do you mean that to properly operate the LM334, we need to apply or reached the threshold voltage of the MOSFET which is around (2 and 4V)? But, i’ve tried to used it (LM334z) as a standalone and still it doesn’t work. maybe the LM334z is the problem hahaha *Regarding the resistor method, What do you think about the measured Vds, Vds=117mV (With an input current of 40uA)? i’m confused with the “how a change in Vds will affect the current” *Isn’t it Vds the parameter required for determining the dose? So if there is a constant current and resistance, how does the radiation affects the MOSFET? Will resistance or current increase upon irradiation leading to an increase in the measured Vds?
You will need to provide a voltage of at least the threshold voltage PLUS the minimum voltage of the LM334Z. If the LM334Z circuit by itself doesn’t work, that will be the first problem to figure out. Make sure you completely read through the datasheet www.ti.com/lit/ds/symlink/lm334.pdf?ts=1689139734…, there are example circuits in it for reference. For the resistor method, keep in mind that the current isn’t constant; the voltage is. Your current is dictated by your resistor and the voltage across it, which is the supply voltage minus the threshold voltage. If your threshold voltage changes as the dose increases (which is the typical behaviour), the voltage across the resistor will change, therefore your current will change, which will generate error in your reading. The only way to minimize this error is to apply a very high voltage (100’s to 1000’s of volts) to the resistor, such that a change in the threshold would become a rounding error.
Unless you've managed to get a switch made out of superconducting material and you're working inside a liquid helium bath, everything has resistance :)
You'll have a bad time trying to measure such low resistances, so usually you can look at the datasheet for the switch you're using or for a similar switch if you need a ballpark number. You'll see an on-resistance, and a max current (since there will be arcing when you open the switch).
If you do want to measure the low resistance, you'll need dedicated meter with a kelvin connection.
Thanks for the feedback and info, I'll know what to look for next time. Unfortunately, I purchased a tattoo pedal as the momentary switch, thinking it would be easier to operate. link Btw. thanks for clarifying everything has resistance, that concept confused me more than I thought it would.
You can calculate a materials resistance using its resistivity and dimensions. For a simple wire, the formula is R = p*l/A, where p is resistivity, l is length, and A is area (cross sectional. Imagine cutting the wire, you'd see a circular cross section).
Some materials like copper have very low resistance.
Some materials like oil have a very high resistance.
Some materials like carbon have a resistance somewhere in between, but generally fairly high.
Resistors use a strip of carbon to make a high resistance path.
Resistance in a switch is typically minimized by design, so introducing a switch or button should not introduce a lot of resistance. It is tyically better not to use switches of this type in signal critical or high power applications (e.g. sound or battery charging), but charging up a small capacitor or powering a small dc circuit should be fine
To measure resistance, one can use a multimeter. This makes use of Ohm's law. Ohms law shows that
V=I*R
Where V is voltage, R is resistance, and I is current. When a small voltage is applied across your component, the current is measured. Then using the current and voltage, it can figure out what the resistance is. It shows it to you on a display so all you have to do is touch the probe tips to the two legs of the switch.
For a switch this will typically be less than 1 ohm. If you buy from a reputable distributor (e.g. digikey, mouser, arrow, farnell, even LCSC) you can get the "datasheet" and look for the constact resistance. This might be a bit harder with ebay/amazon/aliexpress parts, so just stick with a multimeter.
A cheap handheld one is fine, but I'd say prob look for an EEVBlog or other video looking at good cheap meters; you can get pretty good stuff without breaking the bank. Don't stress over it though; any multimeter is better than no multimeter
A 12 volt battery w/ a pot and a few other components. The plan is it wont be running more than 5 milliamps through it. I ended up getting this so not exactly a conventional momentary switch.
That is pretty much exactly a conventional momentary switch. It just happens to be packaged for use controlling something a little different.
It should be fine for your application.
One thing to note - the contacts will probably "bounce" as the switch is closed. Produce a string of momentary connections and disconnections for, oh, say the first few thousandths of a second. That's perfectly normal for a mechanical switch.
That won't matter in its intended application. But if you are using it with electronics, say counting the number of times the switch is operated - the results can be unexpected.
You can look up "debounce" to see how this can be worked-around.
Thanks, I appreciate the clarification on the switch just having a different housing. I'll have to do some further research on "bouncing", interesting stuff.
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