Hardwiring real gauges

[jackpilot]

I just made a small compact pc board for my real gauges. Just sharing the idea.
See picture and diagram

Here is a brief reprint from some earlier posts on the subject

For some of the NG gauges,HYd brake press. fuel temp, air temp...I use real EBay gauges (737 or 727) Basically all like new, cost some $20 each.
1) they look real good and better than any repro
2) they can be made to work with a 5v input (pointer climbing slowly to a preset value)
3) they can be hardwired to whatever switch is supposed to make them alive (no interfacing necessary).
do not pay more than 25-30 . Check on the pictures that the gauge indicates 0. If the pointer is anywhere else, chances are it is no good.
Avoid old yellowish faces. Look for old new stock. And if you are overbid let it go. The turnover is very high and they keep coming back.

The idea is as shown below. You may change the value of the capacitor and of the resistor  according to each specific gauge to make the pointer move slowly ( according to  the capacitor value) up  to its optimum value ( set once for all by rotating the pot)
This is not linked to the simulator, only to a switch like the battery switch or any other appropriate switch.
Good enough for systems which are not simulated.

[Sean]

Nice idea Jack, thanks for posting.

I picked up my first real part on ebay last week, an ACARS unit I hope to use as a keyboard in the sim. I took it to bits and noticed the LEDs for the backlighting. Do you have any idea what voltage they'll be?

[jackpilot]

test with 3V.

[XOrionFE]

This looks great Jack

[Sean]

test with 3V.

Wilco, thx.

[AVIATor-Olav]

Hi.
I know this topic is somewhat aged, but I'll give it a go.
I have a 727 APU unit where I'd like to make the EGT guage come alive. It has 4 pins on the back where pin 3 & 4 says 5v lights. Any idea which pins would make the needle come alive?

Cheers
Tor

[Nat Crea]

It has 4 pins on the back where pin 3 & 4 says 5v lights. Any idea which pins would make the needle come alive?

The other two  (sorry kidding)
But seriously, just apply 3-5v to the other two pins. Usually works UNLESS its a Synchro type gauge.

Nat

[AVIATor-Olav]

Lol. It was the other two pins! I thought maybe they had common ground or something. I touched them with a 5v source and the needle peaked at maximum instantly. Off to buy resistor and capacitor I guess. Anyone have an idea of capacitor size? And I take it that would be for the needle to return slowly to zero after the voltage is turned off?

I'm a bit of a n00b at electronics sorry.

Cheers
Tor

[KyleH]

Yes, the capacitor would slowdown how fast the gauge moves both at turn on and turn off.

The capacitor value shown in the schematic is 2000mF, or 2 Farads. Good luck finding one of those, it would also be the size of a small propane tank.
The one in the picture is 2700uF --> go with that. If you find the needle movement is too fast you can also add more capacitors in parallel to increase the total capacitance.

Make sure you also check that the pot being used can handle the current that the gauge will draw.

[jackpilot]

Capacitor value on the schem. is a typo, sorry
should be 2000uF
All values are approx. The fixed resitor is there as a temporary safety buffer

Once you have the movement OK, turn the pot to reach the max deflection of your choice . measure the pot resistance with a multimeter, add the result to the  buffer resistor value and replace buffer resistor and pot by one single resistor.
Input voltage can be 3v or 5v
-------------
For info:
One handy tool is a spare Power supply from a discarded computer , it will provide 3.2V /5V/12V and it will shut off if you make a short. Handy for testing various electronic devices.

[727737Nut]

EGT gauges operate at mA and mV!!!  You will need a few resistors and caps to really drop the amperage down to make the gauge work.

To piggyback on to Jack's idea, just hook a servo to the pot and you an actual working gauge using a servo card like from phidgets or Opencockpits.  Works great.


Rob

[AVIATor-Olav]

Thanks Rob. I initially thought of doing that, but APU EGT isn't modeled in FS9. I therfore thought I'd just have the needle move at the flick of the APU starter switch as a dummy guage. Haven't decided yet how to go about it. It's a bit int the future anyway, got to interface the FE panel first!


Tor

[N308WA]

Thanks Rob. I initially thought of doing that, but APU EGT isn't modeled in FS9. I therfore thought I'd just have the needle move at the flick of the APU starter switch as a dummy guage. Haven't decided yet how to go about it. It's a bit int the future anyway, got to interface the FE panel first!


Tor

Hello,

It is an old topic but thanks to JackPilot, I am working on wiring the gauges of my overhead and I face the same issue with the EGT APU gauge and the fuel temp gauge from the fuel panel.

How have you solve the control of the low millivolts requested by the APU EGT gauge. I checked that at maximum deviation it draws about 15 milliAmps and about 20 mV.

I also tested the capacitor value : I installed a 2200 microF parallel to the gauge + and -, it definitely dampers the motion of the needle but it keeps oscillating. I would say that instead of 10 oscillations without capacitor, the needle stops oscillating after 4 or 5. Is there an other way to SLOWLY rotate the needle up to the final position without oscillation, or one overshot and then stabilized value (other solution than a huge capacitor... bigger than the overhead itself ;-))

Thanks for reading and helping

Arnaud N308WA

[jackpilot]

It should not be oscillating, try with another gauge.