"Memory" switch - what is the component called?

[robthedon]

Hi all,

Long explanation below but basically I'm just after the name of a component I assume must exist but which I don't know / can't find the name for. It would basically "remember" when it had been turned on until reset later.

Background:

I am trying to create a sort of blackbox recorder in my van. See I run a campervan hire business and have had a few issues where vans have overheated causing very expensive damage, but customers claim that they pulled over as soon as warning lights came on. It's then hard to prove that actually they ignored those lights (though that's the likely scenario) and thus to retain their damage deposits.

Anyway back to the subject. As such I have now bought temperature alarms which buzz when the engines overheat. But what I want to know is can I also buy some sort of component which would "remember" when this happens and which I could reset later if I'm unfortunate enough for this to happen again?

The alarm has a switched supply which, when a temperature is met, could be used to activate a fan or pump. I want to use this to supply power to a kind of "memory" switch which would then "store" the fact that the temperature had been reached. I considered fitting a very weak fuse which would then blow, but there is probably a component that would do it but could be reset later?

Anyone any suggestions?

Many thanks in advance

Rob

[bobnova]

A microcontroller and a real time clock could tell you when it happened down to the second, including how long they ran the engine past that alarm coming on.
I'd hit the Arduino forums (arduino.cc) or the MSP430 forums (43oh.com), one of the two places will probably have someone willing to build one for you.

[robthedon]

Brilliant, thanks a lot, will give that a go. Cheers

[Digerati]

Did you check out the "black box" which already exists in virtually all vehicles? I think I would check the vehicle maker to see what is recorded. I know it already records engine speed, air bag status, breaking status etc. My 2010 F150, when it "sees" I have my phone with me (as it has been Bluetooth paired to my truck) periodically sends a "maintenance report" to Ford. That "suggests" to me more than the last 15 seconds is recorded.

I think it would be a very big mistake on your part if you do not reveal to your customers you have a recording device attached to these vehicles. People - even honest people - do not like to be, and should not be spied upon.

In fact, I think you should bounce this idea off your company's attorney BEFORE installing them! It may be necessary for your customers to sign some disclosure/waiver document saying they are aware it is there (that alone might make sure they do pull over when that idiot light comes on).

So I am not a fan of any deception by any company I do business with. You could look into those Progressive insurance "snapshot" type devices, or something similar - that plug into the diagnostics ports on your vehicles. And then tell your customers it is there to record vehicle status, such as engine temperature, misfires, oil pressure, etc. Perhaps contact your insurance company and see what they suggest.

Above all else, I think it critical your customers know it is there, and why - even one of the reasons is to ensure the vehicles are not being abused.

And slightly OT - a warning light? No temperature gauge? If no gauge, perhaps installing a gauge that sits in the driver's line-of-sight might help. And of course, you need to find out why these vehicles are overheating in the first place. Camper/conversion vans should be able to carry their own load, passengers, and tow a boat and not overheat (in most conditions).

[cypherpunks]

I don't know of a thing exactly like you're asking for, but recording temperatures while goods are being transported or stored is an extremely common application, and there are lots of people selling such devices.

There are "event loggers" that record when a circuit is energized or not. This is more than you ask for, but the easiest commercially available option.

For your application, if you don't have to squeeze every dollar, I'd get a temperature logger with event input so you have both sets of information.

(What you're asking for is basically a bistable multivibrator which can be built out of 2 transistors and 4 resistors to run off of 12V. Turn the whole circuit upside down and use PNP transistors if you need to trigger on a positive-going pulse. And you'll need a reset push-button and a couple of indicator LEDs. And possibly a diode on the trigger line.)

[sergen]

As per the bobnova suggestion check for mentioned links. Definitely you will find some information.