Dollar store window / door alarm - Hacking question

[caphair]

Re: Dollar store window / door alarm - Hacking question

I tried different value capacitors and it actually caused a delay in the alarm sounding and turning off.

[eccerr0r]

Re: Dollar store window / door alarm - Hacking question

yes that would be expected. If you want it to turn on faster with a bigger capacitor, that resistor in parallel needs to be decreased or another resistor in parallel.

These things are really inflexible IMHO... yuck. best you can do for $1.

[redwire]

Re: Dollar store window / door alarm - Hacking question

Pretty sure the alarm is only a reed switch input and a blob chip that generates a simple siren. It has no delay. I think the input cap is for noise immunity given the large 1MEG resistors.

There are extra pins on the IC I think to make different sounds.
These chips usually have an external resistor to set the internal clock speed (for the siren) but this IC has nothing.

People add an extra timer IC then drive the siren IC's input with that.

[earz]

Re: Dollar store window / door alarm - Hacking question

Back from the dead. ��

I picked up one of these alarms today and immediately took it apart. Looks like they’ve changed the circuit. They no longer use a reed switch and have replaced it with a HM6207 Hall Sensor in the bottom right corner. Only component on the backside of the board is the power switch.

[caphair]

Re: Dollar store window / door alarm - Hacking question

Back from the dead. ��

I picked up one of these alarms today and immediately took it apart. Looks like they've changed the circuit. They no longer use a reed switch and have replaced it with a HM6207 Hall Sensor in the bottom right corner. Only component on the backside of the board is the power switch.

Cool. Could these be more easily altered to keep beeping after the door closes?

[eccerr0r]

Re: Dollar store window / door alarm - Hacking question

Doesn't appear so, but if you want to add more components like a 555 or a 4049/4069 and suffer more power loss either version could be modded...

And here's one proposed solution:

[eccerr0r]

Re: Dollar store window / door alarm - Hacking question

Note that the circuit is a redesign of the input to incorporate a delay when the magnet is brought back to the switch.

Btw the input redesign needs to be ... redesigned ... for the hall effect version, though it shouldn't be way too different. The circuit is for the reed switch version. Not having detailed data spec sheet of the YL3710 makes a bit difficult to predict behavior, alas keeping the same type of circuitry helps...

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Another possible redesign to incorporate a delay is to completely do away with the transistor and put a capacitor across the reed switch, and reference the reed switch to GND. Again without detailed spec sheets the behavior is very unpredictable... I suspect they put the transistor there the begin with to deal with noise but ... as said, the spec sheet of the YL3710 lacks the information needed ...