Zero positioning for those teeny little gauges on the EGT and Core RPM gauges

[lesthegrngo]

All, you can never have enough problems to bitch about so I have decided that I want to try and get the tiny little single digit gauges on the A10 EGT and core RPM gauges to work correctly.

 

I have worked out that by dressing the casing of the X27 stepper motors I can just fit them side by side with enough room to allow me to accommodate the axis of the secondary gauge. It is tight, but that bit is doable.

 

The problem is that in common with the altimeter gauge, it is a constant rotation item that requires a zero position sensor in order to work properly. The altimeter is easy as it is a large gauge with plenty of space both behind it for a TCRT5000L optocoupler, and due to the diameter in the gauge face for an unobtrusive slit in the face itself for the optocoupler to work through.

 

The tiny sub gauges don't have the space, so I need to find an alternative. My first though was a hall effect sensor and a 2mm diameter magnet on the pointer, but at that size I believe it will be too inaccurate ( the diameter of the gauge is 15mm) even though I can squeeze the hardware in.

 

Optocouplers need too much space, I can't see how I can get one in there unless there is something like a surface mount device like the SFH9240 IR Sensor SMD Reflective Interrupter. I need to look into the physical size of those to see.

 

So beyond that, are there any other options available for this purpose that would fit?

 

Cheers

 

Les

[No1sonuk]

If you make the rotating part as a drum, you could make it IR-opaque, apart from a tiny slot and construct the opto sensor either side.

 

Alternatively, you could use a layered approach as here:

https://www.flickr.com/photos/jfwall/albums/72157686149623545

[lesthegrngo]

I definitely had a 'woods for the trees' moment there...

 

I had based my thoughts on the design with the nano boards on it, when in actual fact they are no longer there, so I have the space they used to occupy. The optical sensor and hardware will easily fit in the space between the PCB and the back of the gauge face and I just need to make an extension shaft for the pointer with the reflector on it. The Stepper motor itself can sit where the Nanos used to be.

 

Thanks for pointing out what should have been obvious!

 

Cheers

 

Les

[Nikolas_A]

Maybe use air-core motors instead of steppers?

[Deadman]

Gears work get a copy of mikes flight deck first book if you can find it it is out of print Building Simulated Aircraft Instrumentation.Then you may see the woods