RE: Omron HVC-P2 Roadtest - Application Results

Gough Lui — Sun, 25 Nov 2018 05:52:41 GMT

[mention:dc11ece8204f479e8dce2a47a33b20d3:e9ed411860ed4f2ba0265705b8793d05] - just a thought when you mentioned that an image took about 4 seconds to save 320x240. I suspect this is an interface issue - 320x240 @ 8-bit = 76,800 bytes to transfer. At 4.5 seconds, this implies a transfer rate of ~170kbit/s (inc serial start/stop bit overhead). With the 160x120 image @ 8-bit/px = 19,200 bytes to transfer - at 1.2s, this is ~160kbit/s. So it does sound like you have a throughput bottleneck somewhere.

I'm not familiar with the product but the datasheet seems to imply that there is a UART interface and a USB interface which is CDC compliant. In case it is not implemented by a USB-TTL bridge chip, maybe it would be worth hooking up the UART directly to a known good USB-TTL device (like a CP2102/FT-232) to see whether this helps. Also see the code if it's commanding the device to operate at the maximum 921600bps baud rate - although be warned that some devices could be "lost" if you command it to a baud rate you cannot then receive/transmit reliably. At that rate, I'd expect the 320x240 image to only take 0.83s to transmit over the bus assuming full utilisation.

I would expect a Raspberry Pi to not have major issues with storing images, although the Python code could be consuming a lot of CPU time causing overhead. Most SD cards should easily handle a few MB/s. Perhaps try a laptop running Linux?

- Gough