Activity for misk94555
| Type | On... | Excerpt | Status | Date |
|---|---|---|---|---|
| Edit | Post #292872 | Initial revision | — | 28 days ago |
| Question | — |
How does JFET biasing work in a 2-terminal electret condenser microphone? I’m trying to understand the biasing of a 2-terminal electret condenser microphone. The inner workings of a 2-terminal electret microphone are always drawn without a resistor at the JFET source. Is it supposed to be biased like a JFET in a self-bias configuration? If so, how would that work withou... (more) |
— | 28 days ago |
| Edit | Post #291367 |
Post edited: |
— | 7 months ago |
| Edit | Post #291367 | Initial revision | — | 7 months ago |
| Question | — |
What happens when a microSD card is hot-unplugged? Consider a device with a microSD card. The microcontroller writes to the SD card periodically. The operators have an ability to remove the microSD card at any time (they will be removing it every few weeks). Nothing prevents the operators from hot-yanking the microSD card while it’s being written ... (more) |
— | 7 months ago |
| Edit | Post #291083 |
Post edited: |
— | 8 months ago |
| Edit | Post #291083 | Initial revision | — | 8 months ago |
| Question | — |
LED driver with feedback through light. Which feedback topology is better? I’d like to create a stable IR LED light source. I’ve read that LED efficiency changes with temperature. I’ve seen two designs which used feedback through light to correct the LED temperature drift and aging. They used slightly different topologies. The first topology has one feedback loop (thr... (more) |
— | 8 months ago |
| Comment | Post #290874 |
@#36396 I like the idea of an accelerated lifetime test. If I sous vide the sensor in seawater for 2 months at 70°C, that should be equivalent to a year in the field. (Assuming the common rule of thumb that every 10°C accelerates damages by a factor of 2x). I could freeze it a few times along the... (more) |
— | 9 months ago |
| Comment | Post #290874 |
@#8176 **Corrosion.** That’s an interesting question. The electrodes will be ENIG plated. If ENIG isn’t enough, I could do hard gold plating (like PCIe board edge connectors). The metals involved (from top to bottom) are gold, nickel, copper. Gold is a noble metal, so it shouldn’t react with se... (more) |
— | 9 months ago |
| Comment | Post #290874 |
Olin mentioned at the end of his answer that he’s doing an immersed capacitive level sensor, and it works. I bet there are vias, and they aren’t causing too many issues. (At the same time Olin’s situation is different, because he’s not trying to hold water with a PCB.) (more) |
— | 9 months ago |
| Comment | Post #290874 |
@#8176 **Vias.** I can tent the vias with solder mask. I would pick small via diameter (say 0.15-0.20 mm) which would mean that solder mask would plug the vias entirely. That would be the easiest solution, because it’s a bog-standard PCB fab process. If that’s not enough, the PCB fab can plug th... (more) |
— | 9 months ago |
| Comment | Post #290875 |
@#36396 Every 15 to 40 days these sensors will be retrieved. Every year there will be off-season maintenance. The PCB with electrodes can be replaced once a year, if it’s cheap enough. It’s expected that a quarter of these sensors will be lost each year to storms. (more) |
— | 9 months ago |
| Comment | Post #290875 |
@#36396 You mentioned platinum-plated electrodes which dipped into drinking water. I noticed that high-end conductivity sensors use platinum electrodes (low-end sensors use stainless steel). I wonder why platinum? Is there something wrong with gold? [Should I post this to the main board as a sep... (more) |
— | 9 months ago |
| Comment | Post #290874 |
By the way, I’m going to use an [LPS28 pressure sensor](https://www.st.com/en/mems-and-sensors/ilps28qsw.html) to measure depth. Correction for barometric pressure will be done during post-processing. (more) |
— | 9 months ago |
| Comment | Post #290874 |
@#36396 The purpose of the electrodes is to measure conductivity (salinity). I’d like to cover the range from 0.1 to 50 mSiemens/cm (surface water, and seawater). I can settle for 0.1 to 8 mSiemens/cm (surface water only). The device will be completely submerged all the time. (more) |
— | 9 months ago |
| Edit | Post #290874 | Initial revision | — | 9 months ago |
| Question | — |
PCB as a wall of an underwater enclosure Can a circuit board be waterproof enough to form a wall of a waterproof enclosure? Regular PCBs made of FR-4 with solder mask is what I have in mind. But I'm not barring less common PCB materials and processes, although I'd prefer something with moderate cost in moderate quantities. 10m dept... (more) |
— | 9 months ago |
| Edit | Post #289393 | Initial revision | — | over 1 year ago |
| Question | — |
Disabling breakpoints in real-time section of firmware Got a question about hazardous breakpoints in real-time firmware. Does C have a mechanism which lets me mark a section of code such that breakpoints are somehow ignored or not allowed just in that section? I’ve got an STM32 microcontroller which controls an LED flash. The LED current during th... (more) |
— | over 1 year ago |
| Edit | Post #288092 |
Post edited: |
— | over 1 year ago |
| Edit | Post #288844 |
Post edited: I fixed the wrong photodiode polarity, which Olin and Andy pointed out. |
— | over 1 year ago |
| Edit | Post #288844 | Initial revision | — | over 1 year ago |
| Question | — |
Choosing between common-drain JFET amplifier, and common-source Do common-source JFET amplifiers have an advantage over common-drain? The JFET would be in a low noise photodiode amplifier. The signal is 100us pulses with 10us raise times. Here are the schematics which I have in mind. The op-amp would be LTC6252 or LT6200. Single-supply operation is des... (more) |
— | over 1 year ago |
| Comment | Post #288118 |
On a different note, the way the P-channel MOSFET is drawn in this schematic doesn’t look right to me. The source should be on the left. [Common schematic error. I draw a P-channel correctly from a third attempt myself.] (more) |
— | over 1 year ago |
| Comment | Post #288118 |
@#8176 I’m a bit skeptical that a MOSFET drain is sufficiently protected against ESD “for free”. It's true that drain is more resilient against ESD than gate. MOSFETs with higher avalanche ratings are more resilient against ESD to a drain. Nevertheless, I've seen N-channel MOSFETs in an open drai... (more) |
— | over 1 year ago |
| Comment | Post #288118 |
@#8176 The ESD TVS is a fast Zener by nature. How would you choose the breakdown voltage of the ESD TVS? It has to protect the MOSFET, so it needs to be upstream of the MOSFET. At the same time, it needs to survive a load dump. The voltage in the load dump pulse is around 90V, which is orders of... (more) |
— | over 1 year ago |
| Edit | Post #288092 |
Post edited: |
— | over 1 year ago |
| Edit | Post #288092 | Initial revision | — | over 1 year ago |
| Question | — |
DC offset correction loop (DC servo loop). What's its advantage, compared to a high-pass RC filter? Once in a while in literature I see a DC offset subtraction loop. instrumentation amplifier with a DC servo loop Here are a few more examples. DC servo loop removes a DC offset after an op-amp. DC servo loop removes DC current from a photodiode. What are the advantages of such DC offset re... (more) |
— | over 1 year ago |