January 10, 2009 1 Comment
– Rover chasis from RobotShop.ca
– Freeduino from MaxSerial
– Solarbotics motors
– still have the Lego NXT I2C communication cable connected
– IR receiver from a toy
… still building it…
I all of a sudden started to have issues with the MaxSerial Freeduino: it would constantly and spontaneously AUTO-RESET, whenever the RS232 cable was NOT plugged in…
I finally found the solution after some search on the internet, MANY THANKS to SPIFFED for it:
“If you transmit data, while the DB9 shield is unterminated, any activity radiates energy through the shield and into the RX and DTR lines. Since they’re normally pulled low on the RS232 side, transmitting a ‘0’ sends the TX line high, which radiates a high into the DTR and RX lines, the MAX232 inverts this into a low pulse on the reset line, and the chip resets. The solution is simple, connect the DB9 shield to the arduino’s ground, the easiest way is with a short wire/jumper between pin 5 of the connector and the adjacent mounting lug. It’s likely non-kosher to terminate the shield on the DCE end, but it shouldn’t do any harm.
“…RS-232 cable attached via a USB-to-Serial adapter…” Perhaps the USB-to-Serial adaptor is either leaving the shield unterminated or terminating it with a non-trivial impedance to ground.
“…or when the there is no cable attached at all” In this case nothing was terminating the shield.”
It really worked well for me, and you can see the shorting wire between Pin5 and the lug.
“Nasty” problems with the Pololu motor controller… I first used the “low voltage” onethinking that my small motors will need more than 1A each (this “low voltage” version supports up to 5A).
The problem is that when I finally installed it and made it work, I connected it to 9V without realising that the max was 7V !!! Some nice blue smoke resulted, and I had to writedown 40$ losses…
I reordered it, but they didn’t have it in stock (Pololu’s customer service is the best I’ve ever seen… very very helpful and QUICK !) so I ended up with this version which supports higher voltages but only 1A per motor… It turned out his is more than enough, I did some measurements and it never uses more than 200mA !
I actually spent around half a day on making this controller work… don’t worry it’s very easy to use, but ignoring the user’s guide is never a good idea… 🙂 I actually (don’t ask why, there’s no logical reason…) didn’t use the RESET line… It has to be connected and HIGH, otherwise randomly and constantly resets the controller… Once I realised this, everything went smoothly !
A few months, one move from NYC to London and another Pololu motor controller burnt later…
Here’s the LB1836 based Pololu serial motor controller:
|Control interface:||non-inverted TTL serial1|
|Minimum operating voltage:||1.8 V|
|Maximum operating voltage:||9 V|
|Continuous output current per channel:||0.5 A|
|Peak output current per channel:||1 A|
|Maximum PWM frequency:||600 Hz2|
|Minimum logic voltage:||2.5 V|
|Maximum logic voltage:||5.5 V|
|Reverse voltage protection?:||N|