What kinds of caps did you use? I have these caps laying around:

A - electrolytics, Nichion, for c3, c4, c7 (10uF)

B - tantalums, polarized, for c8, c9, c10, c11, c12 (1uF)

For A, is it a big deal they are not tantalum?

For B, is it a big deal to use tantalums instead of ceramic? Polarity for C8, C9, C10 and C11 is obvious. C12 it should be + on the ground side, other side to -VSS? If not I'll find ceramics.

Electrolytics should be fine for the C3/C4 10uf caps, and are non-critical to value.  C7 is spec'd by microchip as a "10uf typical" low-esr cap.  I suspect most modern 10uf caps would work fine.

The 1uf caps can actually be 0.1uf with the MAX3232 I used 1uf as I have a spool of 3K from a hamfest.  I'm sure your tantalums should work fine and it sounds like  you have the polarity correct.

OK, awesome. Thanks for that!

Actually, I'm going to add a 220k resistor as I have 1.1 boards, and use a Sipex SP202E (pin compatible to MAX232). I'll finish it up and let you know how it goes.

3D Case Design 

- VESA mount support

- VGA port to the right

- Serial port to the left

- USB and Power to the bottom

- Vents along the top

- opening to access the baudrate jumper blocks connectors

Any other requirements? Suggestions?

Mike -

All sound great to me!

Ordered v1.1 boards, and from the comments I understand I need to cut the trace to pin 5 and add a 220k resistor.  Anything other mods?

I will work on a 3D case once I have the board assembled.

I've ordered up some of the Rev 1.1 boards from PCBWay and am looking for footprint-compatible VGA, PS/2, and serial port connectors.  Which ones in particular were used in this design?

Ken -

I picked up the connectors a long time ago thru Aliexpress (back when Chinese shipping was quick and cheap).  All are very standard connectors and available thru Mouser or Digikey. 

Hi Gary,

              I have looked through the Max232 & Pic data sheets. It looks to me that 1k0 would be the smallest value of series reistor to use between MAX232 pin 12 & PIC pin 5,  but to allow for tolerances I would suggest trying a 1k5 and then measuring the voltage on the PIC pin to see if it has dropped to around 3v0 . If this resistor is made too big then it will limit the maximum baud rate on receive.   I haven't built my board yet so can't check the voltage myself.     

To get the voltage at PIC pin 5 to drop to 3.5v took 220K between the MAX232 and PIC.  Good news is that it still works fine at 115.2K baud.  I don't know if it pays to use a voltage divider instead of a simple resistor?  Geoff Graham used 100K to 3.3v and 10K in series.

A single trace cut as pictured above, with a 220K resister added dropped the voltage at PIC32 pin 5 to 3.5v on my board, and seems to work nicely.

I have re-done the PCB to use MAX3232 IC powered by the 3V3 rail.  They have been shipped to me and I'll test them when they arrive.

Hopefully this will be the last revision!

Hi Gary,

             Thank you re comments on the Composite RCA socket & for redesigning the PCB.

However, while checking resistor values I have noticed a subtle error.  Pin 4 & 5 of the PIC are NOT 5V tolerant. Their maximum permitted input in Vdd + 0.3 V ie about 3V6. If you look at Geoff Graham's schematic you will see a 10k resistor in the RxD line between CON1 & pin 5 on the PIC. Geoff says this resistor is there in case a 5V TTL adaptor is plugged into CON1 to protect the PIC pin 5.  The subtle fault I noticed is that RxD (pin12) of the MAX232 is connected DIRECTLY to the PIC pin 5. The MAX232 will output 5V on pin 12. There should be a 10k resistor fitted in this line to protect the PIC pin 5. As the MAX232 IC is fitted I don't think you will be able to use CON1 (unless you pull out the MAX232 IC). Thus you could cut the PCB track from pin 12 of the MAX to pin 5 of the PIC & connect it to CON1 pin 2 & so use the existing 10k resistor.

Another possible solution would be to use the MAX3232 IC powered by the 3V3 rail, as this chip would only put out 3V3 on pin 12. C11 in this case would need to go to 3V3 not 5V.

ARGH, always one more bug.  Thank you for being so observant!

I'll try and edit the pcb this weekend and get a revised board fabricated.

I'm measuring 3.9v on RxD (PIC pin 5), so indeed over the 3.6v max.  It does appear to work fine, but needs fixing!

I assume that putting a 10K resistor between PIC pin 5 and MAX232 pin 12 would do the trick?

I did leave the CON1 option in place, but realize that to use it you'd need to remove the MAX232.

Pretty easy to cut the trace on the V1.1 board and solder a 10K resistor on the back of the board.  I'll get some pictures of the changes up later this weekend.

Have you decided on how the design will change for this fix? Is it a single resistor or a voltage divider? What value(s) are needed?

Is there a recommended enclosure to package this project?

I wish someone would design a 3D printable case, but I don't have the expertise.  If anyone is interested in tackling a case please contact me.  I'll gladly provide a working board.

I do not have the PCB yet, but I designed in F360 a preliminary enclosure using the .STEP file generated by KiCAD. Feel free to download and modify it:

https://a360.co/3m9kuES

I have constructed the corrected V1.1 version with the composite output fixed.  It appears to work nicely including the composite output!

Thanks to Williad for spotting the reversed connections to the composite output.  I missed that as I don't use the composite video.  I have generated new gerber files and have upload as V1.1  Be aware that I haven't had a batch fabricated and tested yet - but will shortly.  If you have had boards fabricated from the V1.0 files you could use a short "pigtail" and mount the composite video off of the board with the correct polarity.

I'd consider sharing the Kicad files, I just want to avoid seeing the boards re-labeled and sold commercially.  I'd also rather include any improvements back to this forum if possible.  Contact me privately if you do have a need for the files.

Hi Gary! I had some pcbs made for this project. However when I tried to get a suitable RCA socket for the composite output I found what looks like an error in the Rev 1.0 pcb. It looks like the earth is connected to the centre pin of the RCA jack & the Video is connected to the metal outer of the RCA. If you see this comment please can you check this. Thank you.

Nice work! Would you consider sharing the Kicad project files? This would aid mods to use alternate parts if needed, or other customization.