Tuesday, February 11, 2014

PIC32 Proto Board: Details, Schematic, PCB and Pictures



I previously showed you my PIC32 proto board I made on verroboard (http://tahmidmc.blogspot.com/2014/02/pic32-development-proto-board-on.html). To make the proto board “more of a product” and easy to reproduce, I was working to make the proto board on a PCB.

I used ExpressSCH to draw the schematic, and used ExpressPCB to design the PCB. Once designed, Professor Bruce Land got the PCB made from ExpressPCB themselves.

The PCB is just to be a basic board with the PIC32MX250F128B placed on it. The power supply connections are provided as are external oscillator connections (if needed). Additionally, there is a nice convenient power supply input connector (standard 2.5mm jack/plug). All the IO pins along with power (Vin and +3.3V) and ground are placed on a SIL connector at the edge of the board so that the board can be conveniently placed on a breadboard for experimenting and prototyping (see pictures below).

It's a nice little 2-layer PCB measuring only 3.1 inches by 1.8 inches. I chose to use all through-hole components to make soldering and construction easy for everyone. Now let's look at the schematic, PCB mechanical view and some pictures of the actual PCB itself.

Here is the schematic:
Fig. 1 - Schematic (Click on image to expand/zoom)

Here is a mechanical diagram of the PCB:

 Fig. 2 - Mechanical diagram of PIC32 proto board PCB

You can find the ExpressSCH and ExpressPCB schematic and PCB design files at the end of this article.

There are some key things to note here.

  • Use a ua78M33C or similar regulator for wide range voltage. Use an LDO voltage regulator if there is intention to power off of USB. Be careful about the LDO maximum input voltage rating. Currently, as it stands, the USB is not going to power the microcontroller (at least not reliably) due to the dropout voltage of the ua78M33C regulator. A regulator that can be used in its place so that the board can be powered either off of an external supply or the USB is the MIC2940A-3.3. Here’s the datasheet if you’re interested: http://www.micrel.com/_PDF/mic2940.pdf
  • I used the 0.4in spacing PDIP28 component in ExpressPCB. I used a socket that allowed for that. But you may want to change it to a 0.3in spacing PDIP 28 package. It’s fine and working now. But I will change it in a later revision.
  • C4 is VCAP. It is required for the stable operation of the PIC32MX250F128B. Use a low-ESR capacitor: defined by Microchip as having an ESR lower than 1
  • Mount X1, C6 and C7 onto the PCB only if there is a plan to use the external oscillator. Here the external oscillator is a standard crystal oscillator. If the internal oscillator is being used, don’t mount X1, C6 and C7 so that the associated IO pins can be used. Since the PIC32MX250F128B is only a 28-pin device, every single IO pin is valuable.
  • Variable resistor VR1 is used to supply a variable voltage output to the PIC32MX250F128B pin 26, which is RB15 which is also AN9. This is just to provide a variable voltage to the PIC32MX250F128B for testing with ADC. There is a switch/jumper between the wiper of the variable resistor and the PIC32MX250F128B RB15. When the switch is not closed or the jumper is not shorted, the wiper is disconnected from the PIC32MX250F128B so that RB15 can be used for other purposes, eg external input voltage sensing, use as digital IO, etc.
  • “Debug LED” is connected to RA0 (PORTA bit 0 --> pin 2) of the PIC32MX250F128B.


Here are some pictures of my PCB:

Fig. 3 - PCB just being mounted with components


  Fig. 4 - PCB reverse side


 Fig. 5 - PCB top view (ignore the glare)



Fig. 6 - PCB placed onto breadboard


 Fig. 7 - PCB placed onto breadboard - front view



 Fig. 8 - PCB placed on table - you can see the IO pins



Fig. 9 - PICKIT3 connected to PCB


Here are links to the .sch ExpressSCH schematic file:
https://drive.google.com/file/d/0B4SoPFPRNziHU3pKMFFWSEdWOGs/edit?usp=sharing

You need the ExpressPCB software package to view and edit the .sch and .pcb files. You can get it from here: http://www.expresspcb.com/ExpressPCBHtm/Download.htm

Let me know what you think and I’d love to see what you do with this board. I’ve done quite a few projects with my verroboard proto board and I'll be doing a series of small projects with this board. I’ll post them here from time to time.

9 comments:

  1. I like this blog and its very great that show pictures of PCB

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  2. I need to learn to design PCB . My greatest trouble is producing the Gerber file of a circuit so that I can outsource production of the PCB. Good job Tahmid.
    Please, can you do a tutorial on using the ExpressSCH and ExpressPCB in making PCB. Thanks.

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  3. Hi Tahmid,
    I want to use MOSFET driver IRS2110 to drive MOSFET IRF 540N in power supply design.
    MOSFET switching frequency, I want to keep 20 kHZ. I am obtaining the gating signal using dSpace 1104.
    I have gone through your blog (Using the high-low side driver IR2110).Still I have few question regarding IRS2110.Please help me to answer these questions based on your experience.
    1. Is there any difference between IR 2110 or IRS 2110.I have IRS 2110 available?
    2. What is the maximum switching frequency for which IRS 2110 can be used without any distortion of the pulses? Because I can generate upto 100kHz frequency using dSpace 1104.
    3. As you wrote in your blog that IRS2110 is not an isolated driver. we should connect Vss and COM. What is the harm if we do not connect them?
    Secondly if I want isolation between input pulse and output pulse,How will I get it in case of low-side switch.
    4. I have damaged 5-6 IRS2110.I don’t know what was the reason.I tell you the process what I followed.
    I used the circuit given in Datasheet from IR on PCB.I just applied the same input pulses on Lin and Hin pin and used 0.1uF boost strap capacitor. I didn’t short the Vss and COM (As I was thinking that this driver provides isolation).i used two separate power supplies for VDD (+15V) and VCC (+15V).I saw the ouput pulses on DSO without connecting the pulses to any MOSFET.
    Initially I got the output pulse with same frequency and amplified magnitude but when I repeated the same test, there were no pulses on these pins.
    I don’t know, where I was making mistake!! May be it is due to not connecting the output pulses to switch or may be VDD (+15V).
    Sometime IC also got heated and the VCC supply dropped to 3-4 volt.
    Please help me what mistake I was making.
    5. From datasheet it is not clear that where to connect the ground terminal of Hin and Lin pulses. Is it to connect to VSS?
    6. what should be the boost capacitor value ,if I am using IRF 540N for 20kHz and 20 V output in case of high side driver in zeta converter?
    7.You used additional diode D2,D3 and resistors R2,R3 (10R),is it having value 10ohm or I may use any value like 100ohm or 1 k, how does it vary? and what kind of diode are they. Can I use signal diode 4148?



    Please answer me and help.
    Thanks
    Man Mohan

    ReplyDelete

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  8. Thanks great blog.I was looking at the lab1 in ECE4760 for the capacitance meter that was well done can you post a article with the code for that lab?Thanks Bez

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