Talk:Other Hardware old
Internal pressure sensor
needs access to analog grade psu. scp1000-d11, costs 20-21$ and can provide 10cm (3.3") accuracy with 2Hz update or 1mt (3.3 foot) with 7Hz update rate. The resolution is better. Interface is I2C.
External pressure sensor board (altitude)
--Comm board 07:46, 31 January 2007 (CET)
Pressure Sensor: MPXA6115A MPXH6115A
Interface, 3.3V I2C interface, 100khz, attiny as alternative processor.
- MCU pic12f675 or equivalent
- low cost op-amp (not rail2rail)
- 1Mhz voltage doubler
- Precision 5.0V ldo
- 1x pwm output and at the same time ADC input, 0-3.3V
- 1x raw pressure sensor input, div 1.4 for 0-3.3V range (max resolution is 981 units), optional
- 1x offset adc input (raw-pwm_out)*gain(1000)
- Internal temperature sensor for full temperature compensation outside the 0-70degr. range.
- 16 times oversampling
PDC effort to use Futaba R114F 4 Channel 72MHz RX and "skysport" T4YF 4 channel 72MHx TX
- Opened Receiver and located a Fairchild 74VHC164 Serial-In Parallel-Out Shift Register
- Input (Pins 1 and 2 are wired together) probed using oscilloscope and found odd waveform: Five small triangular waves followed by one large triangular wave. The five small waves change size as the transmitter inputs change:
- The PPM signal is present on pin 9 (clock input)
First picture shows a frame with aileron full right Second picture shows a frame with aileron full left Third picture shows multiple frames (~8ms per frame)
The transmitter has support for only four channels but the top left of the case shows that a place to add a switch. Since the receiver showed five waves and only the first four moved with the controls, I assumed the transmitter PCB probably allowed for a fifth channel.
- Opened the Transmitter and the PCB showed three pads that were clearly meant for a fifth channel.
- To make chan 5 active a jumper had to be populated
- Channel five had a resistor divider network (2x 4.7k) so it looks like it for a switch
- Two position switch would give full signal deflection, Three position switch and two resistors (1.7k) gives decent signal deflection.
- Wired three position switch with resistors and powered everything on to look at receiver serial signal; fifth triangle wave size changes nicely with switch position.