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A Little Diode Problem – Revisited. August 26, 2011

Posted by phoenixcomm in Arduino, DIY Aircraft Cockpit, Flight Simulation, Power Systems, TinyCAD.


Ok Im going to start with a diagram of the power wiring of a typical twin. This twin is going to use 2 automotive engines, that says 12volts but most of the radios etc run on 24volts so I will show you how to do this in a twin. Then once we have this down, then we can implement in our simulator. When we have a mix of 12 and 24 volts, its easier to use 24 volts and we can handle the 12volts with regulators. Ok then on to figure 1.

The Analysis     As you can see we have 3 main buses,  Left, Right, and Battery Bus. We all so have a ground power connection through a Solenoid and that is activated only when both Ground Power/Alternator Field switches are in the Ground Power position, the Master Switch is ON and the Ground Power Cable is connected to the Ground Cart and on.  If you wish to charge the battery the Battery Switch must be on also.

There is also a relay in series with both starting solenoid, which is controlled from one of the circuits on the Master Key (not shown).

There is also a Tie Solenoid, so you have redundant power, the Tie Solenoid is powered from the Battery Bus.

The Plan   Were going to implement this now for our simulator, we need all the switches, and some indicators. So lets get our parts list:

  1. (2) Switch, DPDT, center OFF (Ground Power-Off-Alternator Field)
  2. (1) Switch, Key (Master Key)
  3. (3) Switch, SPST (Battery Switch), (Tie Switch), (Master Switch)
  4. (2) Switch, Push, SPST (Starter Switch)
  5. (9) Resistor, 10k ohm, 1/4 watt.

Lets wire the 2 Ground Power Switches together.  Each switch has two separate sections, lets call them a and b. So you have NO – C – NO, so lets label them 1aNO1 – 1aC – 1aNO2  and 1bNO1 – 1bC – 1bNO2.  So put a wire between 1aNO1 and 2aNO1. 1aC goes to the computer, and 2aC goes to ground. So when you turn on the switch it pulls down. You need to put a 10k ohm resistor from 1aC and power.

Now lets do the other side the Alternator Field, 1bNO2 goes to the computer, and also put in a 10k ohm resitstor to power. Now do the same thing for the 2bNO2. 1bC and 2bC both goes to ground.

Do the same thing for the rest of the switches. One side of the switch goes to the computer, with a 10k resistor, and the other side goes to ground.  So that make a total of 9 inputs to the computer.

You need to have 4 outputs from the computer going to your Master Caution Panel, Right Alt Fail, Left Alt Fail, DC Tie Fail, and Battery Fail.

Optionally you also might want to have a Volt Meter to see the voltage on the different Buss, and if you do you will need a rotatory switch to connect to the different buses.  You really don’t have the buses on a SIM, you need 1 input to the computer for each bus. If you are nuts like me you really use the bus system but instead of alternators, I use two power supplies. And the Field Switch really turns on the AC power. I use another power supply for the ground cart. BTW old PC power supplies work really nice.

You could build this interface with a Arduino, if you used a meter then you could drive it with a H-Bridge, or a DAC and interface it to your sim via usb, or serial.

Ok there you have it, a power subsystem for your twin.  Now you could even expand it even further by hooking up you lights like this, and should all be powered via the Battery Bus:

  • Navigation  NAV ON/OFF
  • Strobe
  • Anti-Collision BEACON ON/OFF

Oh yes I have to put a plug in for TinyCad for doing all your drawings and yes its a free download. http://sourceforge.net/apps/mediawiki/tinycad/index.php?title=TinyCAD


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