Do IT yourself

The source I posted to github directly supports 3 analog input channels.  Airspeed, oil pressure and oil temp, but say you want 1 cht and 4 EGTs?!   Ok, you can do it yourself, and here's how.

Connect the CHT to chanel 4, and 3 EGTS to 5..8.  Install a 1k-ohm resistor to those 5 channels.  Then setup those channels and create a second display page.  When you click the encoder, you'll flip to the second page.  That page will show CHT/EGTs.  You can even show a graph if you use special characters.

Ok... but that's not enough... I need manifold pressure two fuel and all six EGTs and six CHTS. Wowsers! So thats...

• Airspeed
• Oil Temp
• Oil Pres
• Manifold Pressure
• 2x Fuel Level
• 6x EGT
• 6x CHT

It's time to piggyback.  First, make two SportVFR PCB boards, install pass-through header pins and snip all but the I2C pins, power and ground.  Then piggyback the second GPIO board to the first.  Code an I2C slave/master.  The original (first) board will handle the basic I/O and display.  The second board handles the expanded inputs and send them to the primary board as corrected inputs ready for display.

With two boards, you can support up to 16 analog inputs.  

This is a DIY project... You can do  it too, go do it!

Going Pro: Circuit Board

I spent a couple days and built a robust board that can accommodate up to 8 analog or digital channel inputs and 5 dedicated digital inputs.

The primary interface is DB25 PCB mount.  This is the preferred terminator for aircraft use at it is vibration resistant, reasonably priced, highly available and most importantly mechanically-secured multi-terminal connection.

The DB25 connector has 6 ground pins, 3-12v supply, 3-5v internal (500ma max) and all the pinouts for all digital and analog channels.

Supports up to four I2C ports, one is intended for the inertial module and one for the 1602 display. 2 additional I2C ports are available for future expansion.

Quick Wiring Update

This is the rough sketch of the wiring. The sensors either directly read the line (Tachometer & Airspeed) or use a voltage splitter to turn a variable resistance into voltage.  I'll provide the resistances in a later post after I've tested them.

The top terminal is ground & tachometer input
The bottom terminal is system voltage (9-16vdc), airspeed sensor, oil temp and oil pressure respectively.

On the I2C, Yellow is SCL (pin 3 on Pro Micro) and Orange is SDA (pin 2 on Pro Micro)

Putting SportVFR all together

I found a renewed interest in this SportVFR in the purchase of a Pietenpol AirCamper.

Yup... that's me the Yeller-Barron 

The plane came with a full set of your traditional steam gauges they work well enough and I see no reason to replace them (yet).  But, I want to instruct some in the plane.  The front seat has a full set of controls except brakes and any instrumentation.

Period appropriate gauges in the back... Airworthiness/Registration in the front.  No instruments, front seat flying is tricky

 Yup... you get where this is going.  I need a cheap non-certified yet perfectly functional front seat instrument set.  Enter SportVFR.

I spent this weekend wrapping up the project and I think I'm getting very close.  First, I swapped out the MCU.  The prior post suggested a Spark Electron.  I have plans to try that later, but I didn't want my v1.0 to have issues with the EMF the cell transmitter would produce.  I'll have enough problems getting working what I have.

I chose the SparkFun Pro Micro, which is probably the best micro-sized Arduino compatible proto board out there.  It has built in USB Support via the ATMEGA32U4 programming is plug and pray easy.  To be compact, it purposely doesn't pin-out all the GPIO; the 17 provided are more than enough for this modest project. Best of all, they can be had for $5 in small quantity.

So I'm pulling the project together around the Pro-Micro.  Here's the final BOM (drop the test into ebay to find any parts, they all come cheapest or at all from China)

Pro Micr ATMega32U4 5V 16mhz	$4.99
HMC5983 BMP180 Magnetometer / Pressure Module	$3.50
MPXV7008DP Airspeed sensor	$14.98
1602 16x2 Character Display LCD I2C	$3.22
12mm Shaft Rotary Encoder with knob	$3.51
Oil Pressure Sensor 80PSI	$13.98
Oil Temperature Sensor 1/8 NPT	$9.79
HAL Effect sensor NPN	$3.49
Project enclosure with proto board	$5.23
Total	$62.69

At just over $60 with all sensors, this is perhaps an order of magnitude less than anything else out there.

So I assembled it all. I will make a post soon with the full schematic including all the voltage divider resistance values and layout. There was a trick on the Oil Pressure as it has a very low resistance at static pressure. 

Ok, so what does it look like?  It's in an enclosure, it has screw terminals for power and external sensors. I haven't drilled any wholes in the enclosure yet, but I'm just about ready to do that.








Pinout:

I2C - HMC5983, BMP180, 1602 Display (SDA /SCL / VCC / GND

Oil Pressure - Uses multiple resistors to A0
MPXV7002DP Airspeed - A1 direct
Oil Temperature - Uses a Voltage Divider to A2
System Voltage - Voltage divider to A3
Encoder - TBD, I haven't installed it just yet

That's really it! Hard to believe.  The rest is just programming... see the git repository.  The version posted is still in draft form, I will finalize all this soon and post the corrected updates.

Going mobile

I recently received a kick starter project I funded called Spark Electron


I've been scratching my head trying to figure out a useful project for this marvel.  It's uses the digital cell phone system to transmit data to a server where you can easily generate web interactive solutions.

I think I found a useful purpose... SportVFR.  It can transmit telemetry data over the digital cell network.

I see some great uses for this board:

• GPS breadcrumbs digital ELT (emergency locator transmitter)
• Trending data for the engine
• Automatic logbook

By periodically transmitting my GPS location to the server. These can be picked up and in case of off field landing, my emergency contact will be able to direct services to my exact location immediately.

One of the nice things about this board is that it comes with a LiPo battery, and it can be powered by the battery or vehicle power.

The big drawback is cost at $60 and $3/mo for the digital cell service.  While not cheap, what's the price of safety?  And really, I already have the board and need a project for it.