Help establishing a connection BotVac 85 serial with raspi

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Help establishing a connection BotVac 85 serial with raspi

Postby MadAEng » July 9th, 2019, 9:29 am

Hi all,

I'm currently working on a project to integrate a pi zero W in my neato Botvac.
Connecting it by way of a USB cable was pretty straightforward, tried that out according to this method: https://www.instructables.com/id/How-to-Control-a-Neato-Robot-From-a-Raspberry-Pi/

However, since I want to be able to use it differently then in that thread, the USB port was not an option as that didn't fit with the dust bin in.
So, I decided to use the RS232 port on the BotVac board instead, connecting the pi's UART port with a MAX3232 board
https://www.sparkfun.com/products/11189
to convert the signal suitable for the RS232.

The MAX3232 draws its power from the pi and everything is hooked up as follows, with the only differences being that I used the 3V3 pin on the pi, and I don't utilise the 'bottom' part of the BotVac board.
Image
Image
Image

I've disabled the terminal on the pi, and tried to connect to the BotVac using
Code: Select all
sudo screen /dev/ttyS0
(instead of
Code: Select all
sudo screen /dev/ACM0
)

However, whenever I try this, screen is non-responsive to any input and I have to CTRL-A CTRL-D out of it. I figured I may have switched the rx&tx, but switching those is to no avail either.

Does anyone have any clues on where the problem may lie?
MadAEng
 
Posts: 7
Joined: June 26th, 2019, 12:39 pm

Re: Help establishing a connection BotVac 85 serial with ras

Postby valamilamasag » July 10th, 2019, 5:49 pm

MadAEng wrote:Does anyone have any clues on where the problem may lie?


Yes. You just killed the serial port on the botvac in the best case or did unknown amount of other damage to SOC.
Its a 3.3V TTL serial on the botvac, you could have just connected directly to the PI with two 1kohm resistors.
The MAX3232 creates RS232 level voltages which are up to +-15V (30V swing). The SOC on the botvac operates at 3.3V IO voltage and 1.8V (or 1.2V) core voltage, thus anything under 0V (MAX3232 outputs -15V) or over 3.3V (MAX3232 outputs +15V) will damage the SOC.
valamilamasag
 
Posts: 16
Joined: March 19th, 2018, 5:31 pm
Location: Hungary

Re: Help establishing a connection BotVac 85 serial with ras

Postby MadAEng » July 11th, 2019, 5:45 am

valamilamasag wrote:
MadAEng wrote:Does anyone have any clues on where the problem may lie?


Yes. You just killed the serial port on the botvac in the best case or did unknown amount of other damage to SOC.
Its a 3.3V TTL serial on the botvac, you could have just connected directly to the PI with two 1kohm resistors.
The MAX3232 creates RS232 level voltages which are up to +-15V (30V swing). The SOC on the botvac operates at 3.3V IO voltage and 1.8V (or 1.2V) core voltage, thus anything under 0V (MAX3232 outputs -15V) or over 3.3V (MAX3232 outputs +15V) will damage the SOC.


FML, wish someone told me that sooner....

Anyways. thnx for helping me solve that mystery.....
MadAEng
 
Posts: 7
Joined: June 26th, 2019, 12:39 pm

Re: Help establishing a connection BotVac 85 serial with ras

Postby valamilamasag » July 14th, 2019, 1:04 pm

MadAEng wrote: wish someone told me that sooner....


You were told in the other thread. There are countless posts here about that debug interface. You could have easily measured it too, even with a 1 dollar multimeter. Or read what RS232 is and from the measurements quickly determine that it is not RS232.
Alongside where you got the picture in the first post, there is a description about the interface. But pictures look pretty and reading is tiring right?

But I'm curious, did you managed to kill it? Or did one of the ESD/TVS diodes shorted itself and protected the SOC? MAX3232 can only supply a few mA (maybe 15) which if you are lucky sinked away by the protection diodes and dumped into the power line of the SOC.
valamilamasag
 
Posts: 16
Joined: March 19th, 2018, 5:31 pm
Location: Hungary


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