Viewing 8 posts - 1 through 8 (of 8 total)
  • Electronic circuit help
  • molgrips
    Free Member

    I’ve got a car stereo that you can plug USB memory sticks into. Only problem is, I want to plug a USB HD into it. Now this sort of works after a bit of hacking, but the problem is that if you have it plugged in when you start the car, it often doesn’t work.

    I’ve already had to make my own power supply for the HD (using a voltage regulator) but it’s not ideal so I’m going to replace it. However, I want a delay of about say, 90 seconds before the power to the HD comes on.

    This is what I came up with – can someone tell me if I’m anywhere near, or is it bobbins?

    EDIT: thinking about it, for that to work the cap would have to be pretty big, since it doesn’t take much voltage to open the gate, does it?

    IanMunro
    Free Member

    Bobbins I’m afraid. Well it may produce a slight delay (though I haven’t really checked), but to get the transistor to switch 500ma, you’re going to need a current flowing into the base of the transistor of 1-2ma, which will mean an enormous capacitor will be needed.

    Have a google of ‘555 monostable’, as a more typical way of providing what you want.

    glenh
    Free Member

    Yeah, a 555 timer is pretty easy to deal with, and cheap.

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    richmars
    Full Member

    Or, search RS for time delay relay.

    molgrips
    Free Member

    But it was correct in theory, was it? 🙂 I admit that working out the numbers was the next step!

    I remember 555s.. yep.. thanks 🙂

    EDIT relay woudl be simpler tho.. and pre-packaged.

    My plan is to buy a USB mobile phone charger or similar and rip open the insides to get the circuit to step down 12V to 5v – the current voltage regulator is rubbish.

    coffeeking
    Free Member

    Why not just plug the drive in after starting the car? 😆

    scaredypants
    Full Member

    since you’ve rigged a power supply for it, why not incorporate a switch into the line & mount it near the stereo ?

    molgrips
    Free Member

    Why not just plug the drive in after starting the car?

    That’s what I do now, but it involves reaching over to the glovebox whilst driving and is a faff.

    since you’ve rigged a power supply for it, why not incorporate a switch into the line & mount it near the stereo ?

    Thought about this, but it’s annoying, and fiddly. Finding somewhere to mount a switch and making it not look crap would not be easy – and I’d rather it happened automatically than me having to press a button.

Viewing 8 posts - 1 through 8 (of 8 total)

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