<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""></div>I’m trying to finalise the OVMS v3 final board layout, with the factory in China. We have some questions and seek your opinions:<div class=""><div class=""><br class=""></div><div class=""><ol class="MailOutline"><li class=""><u class=""><b class="">CAN transceivers / power</b></u><br class=""><br class="">Overall, the OVMS v3 system runs at 3.3V. We have two power supply sources: USB (where we use a 5V -> 3.3V regulator), and +12V vehicle power (where we use a +12V -> 3.3V switching power supply, to be as energy efficient as possible). Diodes are used for reverse-polarity protection as well as coping with the situation where both usb and vehicle power is applied simultaneously.<br class=""><br class="">Our problem is with the CAN transceivers. I’m used to the MCP2551 (been using it for a decade or more), but that is 5V so greatly complicates the power supply arrangements at the +12V side. We can switch to something like the SN65HVD233 transceiver that works at 3.3V.<br class=""><br class="">But, I am concerned about comments I am reading about 3.3V CAN transceivers and their inability to meet the ISO11898 dominant condition requirement of 3.5V. From my understanding, these 3.3V CAN transceivers get around this by driving CAN-L to 1V, to still get the differential of about 2V (recessive condition?). My concern is compatibility.<br class=""><br class="">What do people think about this? Any recommendations?<br class=""><br class=""></li><li class=""><u class=""><b class="">External Connectors</b></u><br class=""><br class="">The idea is to retain the existing DB9 connector, with the same basic pin arrangement:<br class=""><br class=""><font face="Andale Mono" class=""><span style="font-size: 14px;" class="">DB9-M Signal</span><br class=""><span style="font-size: 14px;" class="">3 Chassis/Power GND</span><br class=""><span style="font-size: 14px;" class="">2 CAN-L (primary)</span><br class=""><span style="font-size: 14px;" class="">7 CAN-H (primary)<br style="font-size: 24px;" class="">4 CAN-L (alternate CAN)</span><br class=""><span style="font-size: 14px;" class="">5 CAN-H (alternate CAN)<br class="">9 +12V Vehicle Power</span></font><br class=""><br class="">That leaves pins #1, #6, and #8 free for expansion uses. It gives us compatibility with existing OVMS cables.<br class=""><br class="">We would then add a second connector. The suggestions here are DB15 normal density, DB25 normal density, or DA-26 high density. My preference is the DA-26 (as DB25 is the old parallel printer style connector and very bulky). As well as power lines, expansion cards could wire to this connector to expose external inputs/outputs.<br class=""><br class="">What do people think about the DA-26 connector? I’m suggesting a female version (as power is carried there, and I don’t want the pins to get pushed together for a short).<br class=""><br class="">Note that we’ve also got a micro-usb socket, as well as space for GPS and GSM/GNS antennas.<br class=""></li></ol></div><div class=""><br class=""></div></div><div class="">Other than that, we are good to go. Things have stabilised now with Espressif, so we can proceed with building developer boards.</div><div class=""><br class=""></div><div class="">Regards, Mark.</div><div class=""><br class=""></div></body></html>