So, since RS232 is pretty antiquated I wanted to get around the need to use a USB to Serial adapter, especially since every off the shelf adapter I've bought seems to either not work at all or be flakey.

This is where that earlier modification of socketing the MAX232 IC (U6) comes into play. My plan was to replace U6 with a second DIP socket with the correct four pins jumpered to pass a TTL signal straight through from the db9 connector to the MS uC. I have an USB to TTL signal converter from Spark Fun, based on the FTDI FT232R IC.

Initial testing of the idea:


3 wire connection, ground, TX and RX:


Test jumpers inside the MS:


Replacement DIP socket to pass TTL coms straight through:


Adapter DIP installed:


While initial testing proved that it works for communications between the MS and the computer, there's an issue with early MSII daughter cards (which mine is) in that if there is no 5V present on the RX pin of the MS II daughter card at power up it goes into bootloader mode. This means that either the breakout board I have always has to be powered up, or a modification needs to be made to apply 5V to the RX pin when it's not powered up. Which is not a problem if I leave the breakout board in the MS all the time, but that was not the plan. I use this board for other devices as well, and I'm too cheap right now to buy another or several. lol So my idea of bypassing the MAX232 IC in the way I wanted was not going to happen. I came up with a few different ways to apply 5V to the RX pin without the breakboard installed, and then disabled once the breakout board was then plugged in, but this would be more proprietary than I wanted. ONLY my adapter would then work with the MS and that will usually not be a problem, but I didn't want to take any chances, so I went with an alternative, I created my own USB to RS232 adapter... well I've breadboarded it so far. I still need to make a more permanent version using some proto board.

My adapter is the same USB to TTL breakout board I used earlier but I'm using another MAX232 IC to convert the TTL levels to RS232 levels that the MAX232 IC inside the MS can then convert back to TTL levels. yeah I know it seems odd to convert up just to convert back down again, but this way if my adapter isn't available for whatever reason and someone else's is, it will still work just as if it were normal. I also have a Blue Tooth TTL board that I used in a school project that I'd like to get working, but need to reprogram the baud rate before I can get that working and I need to look up again how to do that. lol

the overall USB to RS232 adapter breadboarded and communicating:


Just the guts of the main adapter circuit:


I've had this circuit working on my bench for several hours how and it's worked flawless, zero drop outs with my main PC and only a couple drop outs with my laptop, but that's far less than with the USB to serial adapter I tested earlier today which is a Prolific based adapter, which are always flaky at best. I had drop outs every couple of minutes with the Prolific adapter, just monitoring basic coms.