MEP EP#79: Dueling OpAmp Inputs

Podcast Notes

• Parker
  • Article is lagging behind. Will be done on Friday, promise!
  • Rewiring the Jeep Turn signals. The old wiring was interesting.
    • The side marker bulb socket is isolated from ground. One bulb lead goes to the front marker parking lamp positive circuit. The other lead of the side marker is tied into the front marker turn signal positive circuit.
    • When the parking lights are on and the turn signal off, the side marker grounds through the front marker turn signal filament and illuminates the marker lamp.
    • When the turn signal flashes, it interrupts the ground and the marker will flash by dimming. The front marker gets brighter. So they alternate.
    • When the parking lights are off, the filament which the side marker grounds through is reversed. Thus they blink at the same time.
    • This works because of the wattage difference in the side marker and front marker. 4W for the side marker and 24W for the front. High wattage filament looks like a low resistance path to ground and the side marker doesn’t send enough current to turn them on.
    • Problem when you convert to LED. The system works great with LEDs as is. But because LEDs have a voltage drop, they create a little voltage on the turn signal line. This voltage isn’t enough to turn on the turn signal markers up front but it does turn on the indicators on the dash. ANNOYING!
    • Daniel Stern Lightning
    • Parker also experiences diode problem with voltage offset from ground. Punk-a$$ Diodes!
• Stephen
  • Peristaltic pump design – looking into potentially adding this to his brew rig
    • Homebrew pump controlled in loop with proportional valves and flow meter
    • Control flow rate and through put
    • Skateboard ball bearings. A useful, and fancy fidget spinner
  • Craft Beer Pi
    • Going to get a Raspberry Pi programmed up this weekend
    • Wants to use the pump with their interface
  • DS18B20 temp sensor –
    • Have 5 coming in tomorrow
    • Power, ground, and 1 wire signal
    • 9-12 bits
    • -10 +85 Celsius
    • Plugs directly into raspberry pi without anything in between. Craft Beer Pi already has support!
    • Amazon Link
• Pick Of the Week (POW)
  • Measuring Op Amp Input Impedance
    • How to measure various op amps input impedance from DC to a couple of kHz input frequency
    • What about making sure both inputs are equal, regardless of the actual value?
    • Opa-129 unbelievable op-amp. Max of 100 femtoamps – how do you measure that??
  • IoT of happiness? Raspberry Pi Tracks Office Happiness – HackADay
• Rapid Fire Opinion (RFO)
  • Should Stephen and Parker build an IoT of happiness for MacroFab?
  • Poll: Should we have a StarWars Xmas Special Part II? Link to the first Special.

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