12v in-car screen - video signal troubles

[mike_980]

hi everyone! not sure if i will find anything on this forum but thught i'd ask as i was already a member.

Basically I have a board and a screen which I am trying to install in my car for ecu data-logging purposes (small screen in sunvisor would display oil pressure, batt voltage, boost pressure and loads of other stuff thanks to my evoscan software)

The board I have to drive the screen i believe is out of an in car DVD player so I imagine is for 12v. The board also has what i have determined to be a mini din-9 plug which looked exactly like my old sega mega drive 2 plug so i went and bought the cable on ebay and IT FITS!

However, the cable I have is mini din 9 to RCA (yellow, white and red) so the RCA end probably has no means of power input whereas the mini din 9 looks like this:

Sorry that's the best I could find. But as you see it needs a voltage input which I don't believe the RCA has?

Is there another cable I could buy to make my life easier? I am not capable of soldering to a board but i can solder wires together ok so I could buy a cable, cut it and take the wires to the 12v, ground and video input?


If it helps here are some pictures of the board:

Edit: I found this link a while back, it tells me what pin is what but doesn't help me too much with a solution... the guy i bought it from claims is worked on 12v but if it is only for 9v i dont want to blow it so would need a resistor in there somewhere, but i obviously don't know what current the setup will draw... any ideas?

 

[dh390]

I suggest trying to look up the specs for the IC's that are used on the board. This would give possible idea as to an operating voltage.

For testing you could use a 9v battery (or variable power supply) to see if it will work. Then I would suggest using a voltage regulator. The following would be my suggestions.

If you can find it use a LM7809 (or equivlent) fixed 9v regulator in a TO220 case. These are good for abt 1 to 1.5 amp output.


If you can't get a 7809 I would get a LM317 adjustable voltage regulator in the TO220 case. Output current is abt the same as the 78xx series regulators.

Either one should be used with a heatsink for max current output capabilities.

I also suggest fusing the input for short circuit protection to help prevent a possible fire situation in your car.

 

[mike_980]

Thanks for the reply, ok so do you think this part would do?

http://www.ebay.co.uk/itm/1-pcx-L78...362?pt=LH_DefaultDomain_0&hash=item3a83d1518a

It says it can accept voltage inputs of 11.5-25v - my car battery ranges from around 10v (on cranking) to 14.5v (at around 8500RPM), would it be advised to make sure it's turned off during cranking? and if it turns out to run on 9v then this part would eliminate the need for a resistor?

Any ideas on how to physically connect my in car laptops VGA port to the connector on the board and give it a 12v supply WITHOUT the need for me to solder onto the board?

 

[davenn]

hi Mike
that looks OK

keep in mind the max current of 1.2A you don't want to be running it at that continuously
you need to establish what current that unit needs to run before settling on a specific supply

dh390 was a bit generous at ~ 1.5A for the 78xx series regulators that is really pushing them to the extreme.
I have always tried to keep max current through them to ~ 0.75 and 1 A else even heatsunk, they get extremely hot

Dave

 

[mike_980]

thanks

How would i go about finding out the maximum current of my setup?

 

[davenn]

using a multimeter set to amps inline between the positive supply and the board

Dave

 

[dh390]

Dave I have seen some 78xx rated up to 1.5 amp with a good heatsink but it depends on the version & maker. I saw the 1.5A on a 7812 though I don't recall the maker or prefix. The 1.2A would be a good max limit with a good heatsink. These have over temp & current cutoffs built in.

And mike with the 78xx series no resistors are needed. And should be able to get away with only a heatsink for it. Real simple.

This is what I was thinking. See links.

http://www.ebay.com/sch/i.html?_odk...1.R1.TR2.TRC1.A0.XLM7809&_nkw=lm7809&_sacat=0

http://www.ebay.com/itm/5-pcs-L7809...ltDomain_0&hash=item3cb5c2677a#ht_1760wt_1260

These are 3 pin TO220 case devices.

The module you linked to is for use as a power supply with an AC input voltage/source.

What I am talking about is only a $1 max. Plus the cost of a heat sink or you can make a heatsink from some spare aluminum or metal you have. See links.

http://www.ebay.com/sch/i.html?_trk...20+hea&_nkw=to220+heatsink&_sacat=0&_from=R40

http://www.ebay.com/itm/10pcs-TO-22...ltDomain_0&hash=item1c39d34d3b#ht_2550wt_1019

Remember the tab on the regulator is tied/connected to pin 2 (center pin) which is ground/common.