Saturday, May 10, 2014

Field Test - Low Data Rate Transmission

We had a break in the bad weather today long enough to sneak in a test of the low data rate transmit / receive boxes.

Here is the container with the transmitter, Attiny84, battery, and a PCB with two NeoPixels on it. I added them back to the project and found with a shorter strip count I wasn't getting any weird memory behaviors.


It's showing red on the chassis status LED (because it's disconnected) and pulsing the transmitter status LED when a nom (3 bits) is being sent.

Here is a sequence of ever increasing distance, to 100 paces. These images were from the camera in my iPhone 4s and are un cropped, which might help you interpret the scale if you've seen images from the camera before. It's a fairly 'normal' view; not overly telephoto or wide-angle.




This was a decent enough test to give me confidence in 3D printing an enclosure for it.

At 100 paces the receiver would lose lock if my body was between it and the transmitter, but would lock on again if I turned to face it. In practical terms I couldn't really see any detail of the transmitter or it's status LED's at that range, so without onboard video I wouldn't drive the rover from that far away. The battery pack on the transmitter was putting out 4.8v no-load, which is a bit low but within a realistic limit, so this would be a typical maximum range I would expect for line-of-sight use.

The receiver was also in a simple plastic box; with a USB battery, Arduino, receiver, and LCD shield, pictured here:


One obvious thing I found was that I couldn't read the LCD when it was backlit with anything but white. It was red because the transmitter wasn't being updated via I2C, or plugged into the Vex receiver, so it was sending a 'I can't hear anyone' alarm to the receiver, which is one of the conditions that changes the receiver LCD color... I guess it need a NeoPixel status LED for better visibility.

With the Vex RC decoder also completed as part of the package I can go ahead with building up to the first remote controlled drives now... weather permitting!



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