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  1. AnalogKid

    Short term battery backup circuit

    Here is #17 reworked for using the car battery as the holdup power source. I adjusted the values of some components, but without real information about the device being powered they all are guesswork. Did you know back in post #1 that the car battery would be the backup energy source? ak
  2. AnalogKid

    Short term battery backup circuit

    Here is the updated schematic from post #11. R3 and R5 are added to assure that the transistors turn off completely. Note again that some of the component values will change when more is known about the device being powered, the size of the battery, etc. Note also that no lithium battery of...
  3. AnalogKid

    Short term battery backup circuit

    Here is a minimalist concept of a short-term backup with automatic switching. An operating assumption for these numbers is that the 12 V device will operate down to 10 V. R1 limits the peak charging current to something that won't disturb other devices in the vehicle. D1 is beefed up for the...
  4. AnalogKid

    Short term battery backup circuit

    The link brings up a page that requires registration. Also, depending on the current required by the radio, there might be a much more simple way. Basically, it is a version of what is going on with the energy supply to the Q1 base. As mentioned in #12 - if the device current is low, such as...
  5. AnalogKid

    Short term battery backup circuit

    The schematic in #11 is missing one or two resistors. Is there any way to update that post, or do I have to create another post. None of the other fora I'm on have a fixed time period for updates and corrections. Also - if the device current is low enough, B1 could be replaced by a large...
  6. AnalogKid

    Short term battery backup circuit

    Here is a first pass at a *concept* schematic. Most of the components have to be adjusted to fit the actual device parameters. R2 trickle-charges the backup battery whenever the engine is running. D1 disconnects the vehicle electrical system when ignition is off, so those devices do not drain...
  7. AnalogKid

    Short term battery backup circuit

    The first schematic in the page you linked to is both more and less than what you need. The second schematic seems overly complex. And, a relay is overkill. The current or power draw of the device you are powering should be in a datasheet, product page, molded into the case near the power...
  8. AnalogKid

    Help how to build a dc voltage interrupter to control power on and off time. PWN not sutable.

    But I digress . . . Your max overall timing period is 70 seconds. That is a bit long for a simple R-C timer, but not terrible. 1% tolerance resistors are cheap, and 1% tolerance capacitors are reasonably priced at Mouser. The CMOS version of a 555 (LMC555) has much higher input impedances...
  9. AnalogKid

    Help how to build a dc voltage interrupter to control power on and off time. PWN not sutable.

    Hold on there, sparky. "vacuous" - ? Not even close. In fact, his comment conveyed *the value of your response to him* with clarity and precision, so it had useful substance, the exact opposite of a vacuum; something your response to him lacked. He did not understand your response, while you...
  10. AnalogKid

    Help how to build a dc voltage interrupter to control power on and off time. PWN not sutable.

    Completely agree. Now you've stepped in it. When I first started bouncing around forums, it seemed like every other "solution" completely ignored the OP's skill level and/or design requirements, and went straight to either a uC or a 555. Hence, my tagline is "Maslow Antagonist". Here's why...
  11. AnalogKid

    Home assignment

    Once you're done 1 and 2, redraw the schematic in a more conventional manner. Start with the current source to the left, with any resistors directly in parallel with it. Extend the + and - (GND) rails to the right, and then fill in the remaining resistors and equivalent resistors. The +...
  12. AnalogKid

    Help identifying old lab equipment

    Construction suggests a vintage one or two decades older, like pre/post WWII. Could be a precision adjustable resistor peripheral for an analog computer. ak
  13. AnalogKid

    Bench psu build

    PG = Power Good. ak
  14. AnalogKid

    Spectrum analyser Equalizer project how to go about it?

    Impressively steep walls. Corresponding phase plot? ak
  15. AnalogKid

    Spectrum analyser Equalizer project how to go about it?

    In Other Words
  16. AnalogKid

    Spectrum analyser Equalizer project how to go about it?

    The bandpass filters in the article do not have a very narrow frequency response. IOW there is some overlap between the response bands. If you increase the number of bands, the overlap will be worse. For example, if you have one band centered at 1 kHz, and you input a 1 kHz sinewave tone, it...
  17. AnalogKid

    Spectrum analyser Equalizer project how to go about it?

    Upper right - "6 to 12 Volts". ak
  18. AnalogKid

    Spectrum analyser Equalizer project how to go about it?

    He wants 30 frequency bands, each with an LED bar graph, not a single indicator with 30 steps. ak
  19. AnalogKid

    Spectrum analyser Equalizer project how to go about it?

    PDF scans of the magazines. Fun fact - For the same month and year, two different international versions of the same magazine had two different audio spectrum analyzer articles. Hmmm . . . Canada: https://worldradiohistory.com/CANADA/ETI/70s/ETI-CA-1978-06.pdf England...
  20. AnalogKid

    help with a 12v control circuit

    Relay coil current or resistance? Also, what if someone steps on the mat after everything is up and running? Wouldn't the latching relay go to the off state? ak
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