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Topic: nedoCPU-32 - board for PIC32 in DIP28 (Read 32132 times) previous topic - next topic

nedoCPU-32 - board for PIC32 in DIP28

Because now I have PIC32 in DIP28



I decided to design simplest possible board around it that will be "hobbyist-friendly" and "breadboard-ready" ;)

1st approach:

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #1
PIC32MX1XX pinout (* means 5V tolerant):
1* - /MCLR - has reset circuit and connected to X5.1 (VPP of ICSP)
2 - RA0 - connected to X1.1 (A0)
3 - RA1 - connected to X1.2 (A1)
4 - RB0 or PGED1 - connected to X2.1 (B0) and X5.4 (PGD of ICSP)
5 - RB1 or PGEC1 - connected to X2.2 (B1) and X5.5 (PGC of ICSP)
6 - RB2 - connected to X2.3 (B2)
7 - RB3 - connected to X2.4 (B3)
8 - Vss - connected to GND
9 - RA2 or OSC1 - connected to X1.3 (A2)
10 - RA3 or OSC2 - connected to X1.4 (A3)
11 - RB4  - connected to X2.5 (B4)
12 - RA4 - connected to X1.5 (A4)
13 - Vdd - connected to +3.3V
14* - RB5 - connected to X2.6 (B5)
15* - RB6 - connected to X2.7 (B6)
16* - RB7 - connected to X2.8 (B7)
17* - RB8 - connected to X3.1 (C0)
18* - RB9 - connected to X3.2 (C1)
19 - Vss - connected to GND
20 - Vcap
21* - RB10 - connected to X3.3 (C2)
22* - RB11 - connected to X3.4 (C3)
23 - RB12 - connected to X3.5 (C4)
24 - RB13 - connected to X3.6 (C5)
25 - RB14 - connected to X3.7 (C6)
26 - RB15 - connected to X3.8 (C7)
27 - AVss - connected to GND
28 - AVdd - connected to +3.3V

P.S. Probably I should put clamp diodes and current limiting resistors to not-5V-tolerant pins similarly as it's implemented in chipKIT

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #2
why do you have input voltage attached to X1 too ?

I have not seen a datasheet for this pic32 but don't you need a crystal to get max speed? I think you should attach crystal on the board too.

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #3
[quote author="arhi"]why do you have input voltage attached to X1 too ?[/quote]

I may have some boards with 3x8 headers that have some logic on it and +5V power connected to it, so nedoCPU will take that +5V and convert it to +3.3V for PIC32. Alternatively +5V (or unregulated voltage) may be connected to X4 and in that case nedoCPU will provide +5V voltage to the logic board under it (in case of unregulated voltage X1.7 must be disconnected from header - probably I will do jumper for it - and logic board should have its own +5V source or should use +3.3V from X1.5).

[quote author="arhi"]I have not seen a datasheet for this pic32 but don't you need a crystal to get max speed? I think you should attach crystal on the board too.[/quote]

Probably I should - at least as a placeholder for optional crystal. I tried to have simplest possible solution - and it looks like PIC32MX has 8MHz internal oscillator and frequency multiplier (I'm not sure yet how it's working), so it might be enough for first run, no? Also it's 2 I/O pins (RA2 and RA3) that can be used as I/O instead of wasting them to crystal :)

P.S. nedoCPU pinout was born 5 years ago and it was used for this project - it was SX-28 based (nedoCPU-28), then I put PIC16F870 as a heart (nedoCPU-16) and now it's attempt to use PIC32 (nedoCPU-32)...

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #4
If it has internal osc then crystal is not required but yes a header for it should be nice :)

the only other changes I'd personally make on the board (not really required, something I usually add myself) are

1. after a regulator I'd made C2 a ceramic 10uF, and I'd add one 1000uF there in parallel. I have a nasty custom to put a min 470uF and usually a 1000uF capacitor on every board that have mcu on it (prevents a huge number of problems)

2. on all analog inputs I'd add a 3v3 zener diode

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #5
Actually LM1117 datasheet says "10 uF tantalum" on both sides of the regulator (and I've never saw 10uF ceramic)
About 1000 uF - is it OK to have a big capacitor on the right side? If I remember correctly input capacitor must be equal or bigger than output - or this kind of problem only exists for 78xx devices?

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #6
I never had a problem with large output capacitor. As for 10uF ceramic there was a thread on the blog about them, you can get them at farnell, digikey .. for e.g. http://uk.farnell.com/tdk/c3216x5r1a106 ... dp/1844306 it should work way better then tantalum

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #7
[quote author="arhi"]I never had a problem with large output capacitor. As for 10uF ceramic there was a thread on the blog about them, you can get them at farnell, digikey .. for e.g. http://uk.farnell.com/tdk/c3216x5r1a106 ... dp/1844306 it should work way better then tantalum[/quote]

Thanks! I've found them on digikey and it's not so expensive! I will definitely try them...

P.S. What about clamp diodes and current limiting resistors to make all pins 5V tolerate?

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #8
if you want to make all pins 5V tolerable I think it's cheaper to use a buffer then to add bunch of resistors and zeners. Bigger problem is peripherals that might not work with 3v signals (for e.g. bunch of lcd's I have don't recognise 3v3 as high :( ) so you maybe need a level shifter there .. but I believe it's better to make a separate board with level shifter between the existing board and attachments as you want to keep it simple ...

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #9
I can't use buffer because in different applications pins may be used as inputs or as outputs
Also I have tendency to use HCT logic where possible, so its TTL inputs should recognize "high" state of 3.3V pins

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #10
it mostly depends on what's the target use case for the board ... if it is going to be used for dev, I think you can leave it as is (wrt 5v) as you will know what the input and output is and can easily add resistor and zener if your side sends 5v signal to a non 5v line, or you can add buffer or .. or ... but the board itself can stay as is. I'd just add zenners on the analog inputs as those are really sensitive

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #11
It looks like chipKIT has regular clamping diodes, not zeners...

2nd approach:

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #12
those get a whole different type of protection :) and I like to have shottky or other type of fast diodes from line to vdd to kill the garbage on the line but if 5V hitting the line will still hit port too ... a 3v3 zenner to the ground would solve that :)

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #13
I just replicated what chipKIT has on its analog pins

Re: nedoCPU-32 - board for PIC32 in DIP28

Reply #14
Final design of nedoCPU-32 v1.0:





Size of the board is 2.90 x 2.35 inches (74 x 60 mm):





Sources and gerbers were created in Eagle v5.6.0: http://http://nedopc.org/nedopc/32/nedo32v1-eagle.zip (1.2MB)