7809 fixed voltage regulator on a tag strip, but the OP said the camera specifies 8 volts as a supply voltage. Hence I recommended the LM317 based solution.
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13 years ago
Powering camera for longer
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13 years ago
It's not exactly rocket science.....
The impedance of the connection, plus a decoupling capacitor on the input, with a small inductor in series for the paranoid, or, as on the radio power supply input, to kill RF interference.
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13 years ago
Why not just use a higher capacity 9v battery of a different type[1] and make up an output lead which looks like a PP3 battery at the camera end?
[1] Google for 'Lantern Battery' - most are 6v, but quite a few are 9v- Vote on answer
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13 years ago
Why not just buy one of the many reversing cameras on eBay that are designed to run on 12 volts in the first place?
Tim
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13 years ago
True, but there are readily available regulators that are spec'd for automotive applications. Take a look at National's LM2940 and LM2931 series, for example. These will handle the 60 V load-dump transients and are also inherently reverse-polarity safe.
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13 years ago
I was wondering about this - the spec sheet says 8V but the PP3 battery outputs 9V surely?
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13 years ago
Not under load. They're such tiddly cells inside that their internal resistance is quite high.
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13 years ago
So say if I were to run it off a 9V DC supply, say from the mains, it would probably die? Or heat up until it melted?
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13 years ago
I'd be tempted to do what the device says and run it at the stated 8V.
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13 years ago
Yes, me too. But I was wondering what the tolerance would be for such devices, where its a DC adapter plugged into the mains. +/- 1V?
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13 years ago
In message , Jake writes
Does the spec sheet give the permitted min-max volts?
I reckon that 9V will be no problem at all. It's well within the sort of range I would expect an 8V unit to be happy with. The camera is a rubbish design if a mere 9V blows it up.
If you're really worried, stick a diode in series with the supply (between the regulator and the camera. That'll drop you around 0.7V (giving 8.3V)
Of course, if really do want 8V, use (say) a 6V regulator, and jack up the regulator common connection (which normally goes to 0V) to 2V, using a potential divider between the 8V output line and 0V. [Well, that's one way of doing it.]
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13 years ago
In message , Ian Jackson writes
A sudden pile of crap
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13 years ago
I'm sure these things will work from 6 to > 12v quite comfortably
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13 years ago
Like the incredibly crude early transistor radios and rev counters from the '60s? Strange they managed to survive...
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13 years ago
If it is designed to work off a 9 volt alkaline battery, it will work on a wide range of voltages.
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13 years ago
When I took 'em apart after they failed, they all had some form of spike suppression on the power input. Usually a choke and a capacitor. Germanium transistors at that time really, really, needed protection.
The only recurring fault I ever met was on a Philips battery portable with a car dock, which suffered a failure rate of almost 100% on the final IF transformer after 5 yers or so. The dock had suppession components built in, and the failure wasn't related to using it in the car.
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13 years ago
In message , "Dave Plowman (News)" writes
In the 1960s, I made a simply windscreen wiper delay gizmo (one wipe, two wipes, and an adjustable delay between wipes). It worked fine.
I was just about to drill a hole through the dashboard and mount the control potentiometer, when I thought it might be a good idea to try it with the engine running. The wiping simply went berserk.
For some reason, I never got round to remedying the obvious problem, and my gizmo never got used. I've probably still got it somewhere.
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13 years ago
In message , John Williamson wrote
With a car battery that may run up to 14V and the required supply of 8V @ 125mA the device will be dissipating a 1 Watt. This also needs a heatsink and not just a sealed plastic enclosure.
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13 years ago
On the other hand, my 1990s precursor to Sat-Nav was an Amstrad PPC loaded with Autoroute and sitting on the front passenger seat from where I could read the screen. It was plugged into the cigarette lighter socket and never suffered in any way. Mind you, the bloomin' huge smoothing capacitor that I used with it might have had something to do with that.
Nick
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13 years ago
750mW, roughly. Thermal resistance, junction to free air, with no external heat sink, of the TO220FP package used in the kit is 60 C/Watt, so the junction will be at 45 - 50 C above case interior temperature. Within the manufacturer's acceptable limits of 150C for the junction, so make it a metal case, and don't forget the plastic bolt and electrically insulating washer holding the IC to the case, or make it a ventilated box ( Half a dozen 6mm holes top and bottom will do it) if you're paranoid.
The worst case scenario is that the IC's internal protection will shut it down.