7 replies to this topic

[Luke Z]

Ok, so I have a 5byte serial trackball attached through a level converter to my netduino on port 2. The trackball is hard wired for 1200 baud. I seem to be getting dropped bits. For example Hyperterminal on my pc shows: Left click: 131 -> 10000011 Right click: 134 -> 10000110 Debug output from the netduino shows: Left click: 62 -> 111110 Right click: 158 -> 10011110 Is 1200 baud too slow? Do I have messy edges on my serial and need to pull them up or down? Help!

[65tux]

Went through something similar a while back - was getting predictable, repeatable but wrong values back. My issue was not having the correct level shifter - what are you using?

[Paul Newton]

just a guess - it looks like the data may be inverted. What does 5byte refer to?

[Luke Z]

Went through something similar a while back - was getting predictable, repeatable but wrong values back. My issue was not having the correct level shifter - what are you using?

I'm using this level shifter:

https://www.sparkfun.com/products/8745

This is what I mean by 5byte:

http://www.kryslix.com/nsfaq/Q.12.html
The 5 byte Mouse Systems packet section.

[CW2]

How exactly do you have the trackball connected to your PC? Is it connected directly to serial (RS-232) port or do you use any converter? Because if it is connected directly, it has RS-232 levels and you'd need RS-232 <-> 3.3V converter for Netduino (i.e. MAX322x), I don't think Sparkfun's logic level converter (5V <-> 3.3V) works correctly for RS-232 (~ ±10 V).

[Paul Newton]

I agree with CW2 and 65tux, the level shifter you have is for +5V to +3.3V conversion. Not RS232 to 3.3V conversion. What you need is +5V to 0V and -5V to +3.3V e.g. the signal is inverted and the voltage limited. If you only need one way comms (from the trackerball to the Netduino), then you can use a transistor to do the job. Otherwise one of the max232 family will be needed. Have fun - Paul

[Luke Z]

Thanks to all, I see what you are all getting at and that makes perfect sence. I have ordered a couple of these, http://www.robotshop...-adapter-5.html I hope these will fix the issue. I will report back with more.

[Luke Z]

Looks like those 232 to TTL converters I mentioned are working perfectly. only using one pin, but it works well. Thanks for everyones help.