Mini din 7 pcb header/roomba wifi - Page 1
Forum section: electronics / beginners

author: r4ptor
author_rank: Contributor
timestamp: February 07, 2017, 08:49:30 am
content: Hi guys,I'm planning on upgrading my roomba 621 with a wifi module(in this case, a ESP8266). So the current phase is planning, and I got little troubles finding a connector for the roomba.It uses a minin DIN 7 connector(as shownhere). Since I'm very limited in head space, I was planning on doing a direct pcb connection(so directly plugging the pcb in the female connector), but can't find any male headers.Any idea how to solve this? Directly layout the male pins on the pcb and use 1 pin headers(and follow the dimensions suggestedhere)? Strip a cable to get only the connector and solder on some cables?What would be your goto strategy?Also the ESP8266 seems like to be a little diva regarding vcc, I though using a L7805CV(to get the 16V-21V from the battery to 5V) and a voltage divider(2.4k and 4.7k) to get the desired 3.3V. This was my first idea, since i have some L7805CV at home. I know this is not the perfect approach, but since the ESP won't consume much current, my guess was this could work.Am I better of with a 'good' buck converter?Thanks for any suggestions.

author: ebastler
author_rank: Super Contributor
timestamp: February 08, 2017, 07:41:22 am
content: Neat project. I just did a quick check on Google and see that some commercial solutions are available. Is there a DIY project with a ready-made app to control the robot, or do you plan to write that yourself?For the most compact form factor, I would probably go with the pin-layout-on-PCB option. Nothing wrong with that, as long as you plan to leave the PCB permanently installed. (If you keep plugging and unplugging it, the mechanical strain may get to the solder connections over time.)For the power supply, definitely implement a proper step-down converter! While theaveragepower consumption of an ESP8266 is indeed low in typical applications (where it remains asleep most of the time), thepeakcurrent can be 300mA or so at 3.3V. You would need to buffer the supply with an inconveniently big capacitor, and/or use inconveniently low resistors in your voltage divider, if you wanted to make your passive divider approach work. Little AMS1117 step-down converter modules are available on ebay for next to nothing. However, I have not found a converter that can directly step down from around 20V to 3.3V (during a very superficial search), so you may need a two-stage conversion.I understand that you will also need to bring the serial data line down from 5V (coming out of the Roomba) to 3.3V, as the ESP8266 inputs are not 5V tolerant. For this, a voltage divider with the dimensioning you mention should be perfectly adequate.

author: r4ptor
author_rank: Contributor
timestamp: February 08, 2017, 10:11:09 am
content: Thanks for the reply.Yes, I'm aware of the already made and buy able solutions, but I don't want to spend 100$ on it, and it could be a funny little project. And yes, I'm planning to code all that stuff by myself, shouldn't be that hard.The board will be connected permanently, so the pcb mount solution looks like the way to go. Regarding the supply voltage, I did dig a little bit deeper and found theLM1086CSX-33.Input Voltage MAX: 30 V,Output Voltage: 3.3 V,Output Current: 1.5 Alooks good for me. I don't think it will get very hot, but just in case I thought about a little heat dissipation area on the pcb. Should do the trick.As far as the serial line goes, well I didn't even think about that, I was only concerned about the power supply, thank you for the hint.

author: ebastler
author_rank: Super Contributor
timestamp: February 08, 2017, 11:11:12 am
content: Come to think of it, maybe the better connector solution would be to take a plug apart and use its insert -- something like this:http://www.4uconnector.com/online/graph.asp?graph=0910.jpg(Not the right type of plug, but I assume you can get the 7-pin plugs?)Create the plug foot print on the PCB, and solder in the connector block (instead of separate pins). The molded plastic around the pins will give them better mechanical support. And maybe you need a little vertical spacer anyway, to get the PCB clear of the Roomba's enclosure?The LM1086CSX-33 should be fine, as long as you can program the ESP8266 to transmit with a low duty cycle. You probably don't want to sustain the peak dissipated power of 4 to 5W for too long.Good luck -- sounds like a fun project!