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  1. AnalogKid

    Simple Hall sensor alarm circuit?

    Yes. The 10 K resistor protects the reed switch contacts. When the switch is open, R1 charges up C1 to 9 V. This takes a several seconds because R1 is so large. When the switch closes, all of the charge in C1 is dumped through it in microseconds. Even though it is very brief, this can be a...
  2. AnalogKid

    Want to make a box that will open at a programmed time.

    https://www.ebay.com/itm/394863187122?itmmeta=01HTT4044SM5HQFJQK4A3TYZRM&hash=item5befae14b2:g:qWAAAOSwh4NlUxQr&itmprp=enc%3AAQAJAAAA4IuhgXTE4ijikRGNo9CkfL2SA1CKTFFwLB%2FUFi4%2FLDknK%2FppMMECrjJ%2FrsG1XDk4nE8Ax4ngkdAU0pPu1Kzgj8xlk3EwN8qSDICxJoh5%2F2sNISsGZ43lt53lfF6BOch46yJs2f7auQW236djxTt5O%2B%2...
  3. AnalogKid

    Want to make a box that will open at a programmed time.

    You said you like making things out of wood, so . . . ak
  4. AnalogKid

    Want to make a box that will open at a programmed time.

    Think about this. A spring-loaded lid that pops open when a latch is retracted. A small solenoid connected to the latch. A small wall-wart type power supply to power the solenoid. A lamp timer. A 3 am, the timer powers the wall-wart, which powers the solenoid, which retracts the latch. For a...
  5. AnalogKid

    circuit breaker alarm

    First, you have discovered a great truth - m-m-m-m-Many of the circuits on the innergoogle are intentional garbage. But there is an alternative. It is with great trepidation that I do this, because for an undisciplined soul this can be free crack cocaine...
  6. AnalogKid

    circuit breaker alarm

    A photodiode is not a fully integrated IR receiver; it's just a diode. It sees all ambient light of all frequencies from all sources. If any of it is in the right frequency range, it responds. It is common for a circuit like this to work in a dark room, but fail when the sun comes up because...
  7. AnalogKid

    circuit breaker alarm

    The #1 schematic shows 1/2 of an LM358 for the opamp, and you mention the LM358 in other posts. BUT . . . The opamp in post #16 is a 741, and the wiring is correct for a 741. However, a 741 will not run correctly on 5 V. Per the datasheet, the minimum Vcc is 10 V (or +/-5 V). The photo also...
  8. AnalogKid

    circuit breaker alarm

    Increase the 10 K bias resistor to 100 K or 1 M. That still might not be enough. Do you have a DMM or scope? ak
  9. AnalogKid

    circuit breaker alarm

    First guess, the photodiode is not passing enough current to pull up the non0inverting input above the pot setpoint. Pin 5 is low >> pin 7 is low >> buzzer is on. Link to the original circuit page - ? ak
  10. AnalogKid

    .5 delay with a 555 timer

    The circuit, complete with component values, is in the datasheet. If you can read, you can cook. ak
  11. AnalogKid

    Auto shut off circuit

    My schematic software does not show power and GND connections to logic devices. I should have pointed that out to the TS. oops. C2 is the power supply decoupling capacitor. It connects to the device Vcc and GND pins with the shortest possible leads. Most ICs require power supply impedance...
  12. AnalogKid

    Auto shut off circuit

    Here is the same circuit using a 555, with the timing capacitor in its traditional location. Note that while a bipolar 555 output stage is extra-beefy, it is not super efficient. At your load current and a 12 V operating supply, the voltage across the siren will be around 10 V, not 12. Still...
  13. AnalogKid

    Auto shut off circuit

    While you were typing, I updated the post with an improved schematic. In almost all R-C timer circuits, a capacitor is charged "up" through a resistor. Over a time period, the voltage across the cap steadily (but not linearly) increases until it equals the supply voltage. Actually, the...
  14. AnalogKid

    Auto shut off circuit

    Turns out I already answered this two years ago on another forum. Here is that schematic, re-worked for your application. This circuit powers the load for approx. 44 seconds. R1and C1 set the delay. R2 and D1 provide a rapid discharge path for C1 when power is removed, so it doesn't take the...
  15. AnalogKid

    Auto shut off circuit

    The siren draws 120 mA at 12 V, which is within the capabilities of a standard 555 without an external driver transistor. Based on your responses, a single 555 should do what you want. Schematic to follow. However, this also can be done with just 1 transistor, a small-signal MOSFET like the...
  16. AnalogKid

    Auto shut off circuit

    Please clarify your question. Do you mean that you want the siren to come on immediately when power is applied, and they turn off after 30-60 seconds? Then what? Does the siren remain silent until power is removed and reapplied? What is the voltage for the timer circuit? What is the...
  17. AnalogKid

    Building a tilt sensor with an audible alarm...

    What is the power source? What is the alarm/beeper? The loudness and amount of power determines part of the circuit. How long is the delay before it starts beeping? How long does it beep before it shuts itself off? Or does it beep forever until the sensor is un-tilted? Do you want to build...
  18. AnalogKid

    Simple Hall sensor alarm circuit?

    Usually, what's inside the switch module is a hermetically sealed reed switch. In that application, good for decades - depending on quality. In a security application, the switch is usually closed 99.99% of the time. If the reeds have even a tiny bit of ferromagnetic content they can become...
  19. AnalogKid

    Question about DC current flow

    I prefer electron flow. ak
  20. AnalogKid

    Simple Hall sensor alarm circuit?

    That is a piezo beeper, not a buzzer. There are two types. One is just the bare piezo element, and requires an AC driving signal. The other has an oscillator circuit built-in, and runs on DC. This is what you have. It is a very low-current beeper, so just about any small-signal transistor...
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