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  1. pgib8

    Unbalanced super capacitors in series

    Something new to me is that when you put 2 (or more) supercaps in series that one of them could reach a higher voltage than the other and possibly exceed its rated voltage. It appears there are 2 mechanisms by which this happens, one is variance in capacitance and the other is variance in...
  2. pgib8

    Pi/L filter versus impedance matching network the same?

    Hi everyone. I'm familiar with impedance matching of antennas via a series element and a shunt element but i'm not familiar with filters. When I look at the two side by side they look exactly the same. For instance I used from the source to a 3.3pF series capacitor followed by a 12nH shunt...
  3. pgib8

    Math Question, How Do You Really Figure This Out

    I wasn't going to put in the title how to calculate LED current, but that's what this is. I subtract the Forward voltage from the supply voltage. Let's say for this white LED it's 3.4V - 3V. I'm left with an extra 0.4V, which I run by the current limiting resistor. In this case 13.15 Ohm. So I...
  4. pgib8

    RF Field of PCB trace antenna

    Hi, I drew two types of PCB trace antennas in MS Paint (the best I can do for now). The PCB would be mounted on it's side, so you're essentially looking at a vertical monopole with poor ground plane. I intuitively drew in both magnetic (H) and electric (E) field lines, the way I think they...
  5. pgib8

    another bad circuit

    Hi. I came across another bad circuit at my work. It's producing a ridiculous amount of noise and actually failed conducted and/or radiated emissions during UL certification. This project is not under my responsibility and I'm sharing it because I would like to hear your opinion, to provide you...
  6. pgib8

    Mind-boggling schematic of power supply.

    I came across the schematic of a power supply at my work. The "engineer" that designed it doesn't work here anymore and as far as the company is concerned the design is fine. There was an "anomaly" that prompted my attention. I spent several days trying to figure out what was going on to no...
  7. pgib8

    RF question for multiple transceivers on one antenna

    Hi! I'm thinking about how one would integrate 3 transceivers on a single antenna, in such a way that in TX mode only one transceiver will ever transmit, and in RX mode, all 3 transceivers will be listening on 3 independent frequencies at the same time. Attached is the concept I'm thinking of...
  8. pgib8

    Curious inductor question

    Inductors present a higher resistance to higher frequencies. I'm sending a sine wave through an inductor measuring input and output. Strangely the voltage at the output increases with frequency rather than get smaller. The key for this to work is with no load. Even a 30K resistor will stop this...
  9. pgib8

    pcb trace, common-mode noise, and murphy

    I’m looking at this circuit board that has inputs from a reed switch. Everything is mounted in a panel which contains 240 VAC. The cable for the reed switch is like 6 feet in length and twisted. When I switch current through this panel, the cable I’m talking about picks up noise which I’m sure...
  10. pgib8

    BIOS being replaced

    I just read about UEFI replacing old-school BIOS in computers. UEFI can support remote diagnostics and repair of computers, even with no operating system installed. translate? UEFI provides remote access to your computer at the deepest level (think: turn on camera without LED coming on), and...
  11. pgib8

    tuned (tank) circuit, oscillator, Q

    Hi! I've been wrapping my head around the beautiful and magical workings of tuned circuits and everything about inductance and capacitance. For a tuned circuit I understand (and btw. i'm specifically referring to parallel LC), that any combination of capacitor and inductor will have one and...
  12. pgib8

    clever I2C/SPI switch: fail

    I'm working with a microcontroller where I had to select the small version with fewest pins to save space. So now I have I2C and SPI sharing some of the same pins. If I want to use both, it's easy in firmware but more difficult on the hardware side. The SPI device(s) won't be an issue because...
  13. pgib8

    Voltage divider protected by Zener diode

    I'm looking for a voltage divider that also has its output clipped at about 3V. I need to do voltage measurement and I'm going to use a voltage divider. I want to "magnify" the lower region. The input is 0 to 20V but I'm really interested in 0 to 4.2V (Li-Ion battery). So I thought I use a...
  14. pgib8

    clever vibration motor driver?

    Hi, I'm doing a little circuit to drive a small vibration motor. I want to be able to control the voltage that feeds the motor and of course to be able to turn it on and off. I'm using a microcontroller and digital-to-analog converter. My first idea was to use an OP amp after the DAC as voltage...
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