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  1. hevans1944

    Over voltage protection.

    Agreed. Always do some research before diving over the cliff to discover the hidden rocks under the water. This is called "due diligence" in lawyer-speak. You might even decide not to jump, and hire someone else to jump instead.:D Power supplies are normally used anywhere from a minimum load...
  2. hevans1944

    Over voltage protection.

    Doesn't really matter how fast or slow the fuse or circuit breaker is if you are using a crow-bar for protection. If you are crow-barring the protected circuit, the crow-bar current will have already reduced the supply voltage to a safe value, and it continues to do so, no matter how long it...
  3. hevans1944

    Electromagnet with strength controlled by photoresistor

    You can run longish 24 AWG stranded wires from the Arduino common to the MOSFET source terminals and from the Arduino output to the gates of the MOSFETs. These wires will carry the current required to charge and discharge the gate capacitance when you turn the MOSFETs on and off. When you wire...
  4. hevans1944

    Problems with transistor on test circuit (beginner)

    I read your posts, but wasn't sure if you had moved the motor to the collector and had increased the value of the base resistor. Both are necessary and sufficient to operate the motor from a Raspberry Pi output. The only reasons I can think of to use (or need) a relay is (1) if one of the motor...
  5. hevans1944

    Help making remote control LED lights

    Yeah, I have one of these I installed years ago instead of wiring up the defunct door-bell/chimes circuit that failed thirty-something years ago. Small battery in the push-button switch has lasted for years. The plug-into-the-wall outlet receiver is located in the kitchen about thirty feet (ten...
  6. hevans1944

    Problems with transistor on test circuit (beginner)

    Are you still trying to use the motor connected to the emitter? If so, it will never have a voltage across it greater than the base drive voltage minus the base-emitter forward-biased junction voltage drop. The transistor will never be saturated with the motor in the emitter lead. You must move...
  7. hevans1944

    Over voltage protection.

    Make sure the crowbar sinks enough current to blow the fuse or to trip a reset-able circuit breaker.
  8. hevans1944

    Help making remote control LED lights

    You appear to need multiple transmitters networked to a single receiver, each transmitter being uniquely identified by the receiver. An Arduino and an XBee module, six of them, will suffice for all of these requirements. The remotes each contain an Arduino and an XBee "shield" powered from four...
  9. hevans1944

    Electromagnet with strength controlled by photoresistor

    The proof of concept video was pretty cool! Congratulations! OTOH, the ferromagnetic "speed nuts" should probably be avoided. I would recommend using all aluminum hardware, or nylon all-thread with nylon nuts. From what I've read on Amazon, the ferrofluid will be "attracted" to any ferrous...
  10. hevans1944

    Stepper Motor Max RPM

    And this is why PWM supplies for stepper motors are the preferred drive paradigm. If the winding insulation can stand for it, it is not uncommon for PWM supplies to deliver pulses with amplitudes ten to a hundred times greater than the motor's rated voltage. So, a low-voltage (2 V), low...
  11. hevans1944

    Electromagnet with strength controlled by photoresistor

    Yes.
  12. hevans1944

    zigbee module

    Lots more information is available on this page. Download the DATASHEETS referenced near the bottom of the page and read them. Do your own homework! Reading the RSSI value requires access to control registers in the RFM75 data modem via its 4-pin SPI data link. The documentation may tell you...
  13. hevans1944

    Electromagnet with strength controlled by photoresistor

    Wow! Did you make sure you scraped all the dust off that MOSFET before hooking it up? Datasheet says this is 1999 technology. The Rd(on) is pretty high... 0.1 ohms. That's still too low to accurately measure with a two-lead resistance measurement, unless you "nulled out" the meter lead...
  14. hevans1944

    Electromagnet with strength controlled by photoresistor

    It was late when I wrote that. I went back and changed all references to Gds to Vgs. Yes, it will probably work okay. Rd(on) will be a wee bit larger because the gate drive is smaller. I think it does, but I have no first-hand experience with actual measurements of Arduino output drive...
  15. hevans1944

    Electromagnet with strength controlled by photoresistor

    Semiconductor manufacturing at a profit is very much dependent on "yield" from any particular wafer. There are many process parameters that, if slightly incorrect, can affect yield to particular test specifications. The location of a part on the wafer (center versus edge) can also be a factor...
  16. hevans1944

    Electromagnet with strength controlled by photoresistor

    Look at Figure 2. Transfer Characteristics for the document you reference (Fairchild FQP30N06L N-Channel QFET datasheet): Note the drain current scale is logarithmic. At 25° C, for Vds=25 V, the drain current varies from about one ampere, near the Vgs threshold of about 2.3 V, to about 10...
  17. hevans1944

    Help me identify this

    The board you are trying to replicate is used in lieu of a much more expensive ($595) simulated avionics hardware module used with the X-Plane flight simulation software to provide user-control inputs to a simulated cockpit-mounted Garmin 430 GPS, visible in the background screen above and...
  18. hevans1944

    Electromagnet with strength controlled by photoresistor

    Yes. Yes, you're good to use the 1N4001 to block the power supply voltage. Yes. Yes. I believe all diodes in this series are manufactured from the same chips which are diced from a wafer, packaged, and tested for sorting into "bins" by their maximum peak reverse voltage. In actuality...
  19. hevans1944

    Electromagnet with strength controlled by photoresistor

    The diodes need a peak-inverse-voltage (PIV) somewhat greater than the power supply voltage applied to the coils. When the MOSFET turns off, whatever the current is in the coil at that moment will be transferred to the diode, so the peak current capacity of the diode needs to be at least as...
  20. hevans1944

    Electromagnet with strength controlled by photoresistor

    If you can find some threaded bolts of appropriate diameter, perhaps made of mild steel (iron would be better) you can heat them with a blow torch to incandescent red temperature and then allow them to slowly cool. This will "temper" and soften the steel, possibly making it more permeable to the...
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