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  1. AnalogKid

    Need Help Creating a digital display that counts and saves numbers

    Much as I hate to say it, this project screams PIC, one of their super low power critters and a serial input LCD display. That gets you flash memory for the total count, a battery-save timer, etc. What you really want is for the watch IC wizards at Casio or Citizen to whip up a counter chip...
  2. AnalogKid

    D Flip Flop Question

    First, I would think that the 555 would drive the clock input, not the enable. Second, thee is no enable input to a 7474. So answering your question will be difficult until you provide better information. And a schematic. In an electronics forum, *everything* revolves around the schematic...
  3. AnalogKid

    1.5v - 100V input.

    OR, since you don't care what the input voltage is above the 1.5 V threshold, bring it into the input of a comparator through a series resistor and have a shunt zener to GND. For example, have a 100 K series resistor and a 5.1 V zener. It acts as a zener regulator when the input is above 5.1...
  4. AnalogKid

    Need help with school project; photocell, op amp, and 555 timer

    Depends on the opamp. A 741 output can't get to less than about 1.5 Volts away from either rail. If you replace L1 with an NPN transistor with its emitter tied to GND, then its collector can drive a small relay. But you have to put a signal diode across the emitter-base to prevent reverse...
  5. AnalogKid

    Need help with school project; photocell, op amp, and 555 timer

    The photo is nice, but in electronics, "show us your circuit" means show us the schematics. It sounds like you're most of the way there except for some kind of interface. Show us your circuit. ak
  6. AnalogKid

    Need help with school project; photocell, op amp, and 555 timer

    You could use the 555 as an oscillator to drive the laser, and configure the opamp as a bandpass filter to detect it while rejecting ambient light interference. ak
  7. AnalogKid

    4 players quiz game using relays

    Improvement. ak
  8. AnalogKid

    Need help with school project; photocell, op amp, and 555 timer

    Or, you are too stupid to understand him. Think horses,not zebras. ak
  9. AnalogKid

    Ultrasonic Metronome, or rangefinder transmitter

    So two astable multivibrators, or oscillators. One slow, and it gates the fast one briefly. Two CMOS 555's will do this, or a CD4093 or CD40106, etc. First thing is to decide on the transducer. Everything flows from that. aj
  10. AnalogKid

    Regulate from 12v to 3v?

    The coin cell can be 3.6 V, so 3.3V is right in the middle of a good range for anything powered by one. 3.3V is a common power regulator output value because it is one of the standard power voltage values for newer digital logic chips. ak
  11. AnalogKid

    Reed switch

    In a security system for a home, usually groups of doors or windows are combined. For example, all of the windows on the 2nd floor are connected together in a series string of switches. As long as all of the windows are closed, the loop is closed. If any window opens, the loop opens and...
  12. AnalogKid

    Powering a mobile FM transmitter

    That's 50 us (microseconds) and 75 us. ak
  13. AnalogKid

    Powering a mobile FM transmitter

    If the AC power adapter is rated for 2 A continuous duty, then the radio must draw less than that. 24 W of DC for a 7 W transmitter means that the unit is less than 30% efficient, a low number. 1.5 A for 4 hours is a 6 A-h, 12 V SLA battery. Digi-Key has a 5 A-h unit for $25, and a 7 A-h unit...
  14. AnalogKid

    reversed photodioded LED? help out! simple!

    Close. The capacitor C should be replaced with a straight wire. Connect the NPN base to the PNP collector. Also, to make things easier to discuss, spread out the parts on the schematic and add reference designators (R1, Q2, etc.) to each component. Have you calculated the values of any of...
  15. AnalogKid

    Reed switch

    The switch itself is normally open. It is held closed by the magnet on the door jamb or window frame. The switch opens when the door is opened, the loop opens if a wire is cut, etc. No matter what the cause, open = alarm. The next layer of sophistication is to put a resistor across the...
  16. AnalogKid

    reversed photodioded LED? help out! simple!

    Do you mean that you want the brightness of the LED to increase when the light hitting the photodiode decreases? Also, what is the photodiode part number? ak
  17. AnalogKid

    SUPERCAPACITORS

    Three things. First, any - ANY - form of energy conversion creates more pollution. All conversion methods are less than 100% efficient, which means that your plan will have exactly the opposite effect of what you want. Second, an automobile engine is reasonably efficient at moving two tons of...
  18. AnalogKid

    Help required for Linear Power Supply build using LM317

    Check the 317 pinout. The adjust pin is in the middoe of the schematic symbol, but not the device. Also, note that on the original National Semiconductor datasheets they frequently showed devices from a bottom-side view. Statistically, the #1 problem with new linear regulator designs is the...
  19. AnalogKid

    4 players quiz game using relays

    I have praised that circuit in the past. One of the best pieces of logic design ever. ak
  20. AnalogKid

    Reed switch

    That is a standard, simple reed switch and a magnet. For a door or window or whatever, the magnet goes on the moving part and the switch goes on the frame or jamb or whatever the stationary part is. The switch doesn't "require" any particular voltage or current. It probably has voltage and...
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