Brads Electronic Projects Forum

Im working on a PIC project board that can be used to program and test PICs and circuits. I have a small design built on some protoboard, but Im trying to make a pcb that would look nicer and have more functions. Im designing it in a "modular" form. This meaning that each section of the board is not connected internally. This will allow different PICs to be placed on the board and only have to move some wires around to make it work. I will use a 40 pin ZIF universal socket to hold the PICs. Im planning on there being a way to set up the ports in different spots so that on longer projects or projects that use the same pic you can not have to do everything off of pin numbers. This would really just be a 16 pin header with the two sides cross connected in an "in and out" form. The "modules" that I have thought of so far are, an 8bit led array, an 8 bit DIP switch, a couple of seven segment displays, a pickit connection, a rs232 converter, usb conector, clock slot,and a piezo speaker. I will make a base for it and glue a piece of breadboard to the bottom for simple circuits. If you guys have any ideas on any more things that I should add let me know. Once I get a basic design of the pcb I will post it here but I wanted to get the idea out while I was thinking about it. Also if someone has more information on how the MAX232 chip works or a circuit for it.

Every hobbyiest needs their own practical development board - lots of learning curves and enjoyment along the way

Digg wrote:Also if someone has more information on how the MAX232 chip works or a circuit for it.

I wrote an article a long time ago when I first started using the MAX232 - perhaps I should update it someday?

You can find it in the Swordfish Code Examples section at Digital DIY

Digg wrote:If you guys have any ideas on any more things that I should add let me know.

Sounds like a great project Digg, How about a connection for a LCD display?

Such a great idea!

I would definitely look at including an LCD display of some sort. 16x2 would be perfect and they cost as little as $4 with free postage.

Maybe even a keypad and a few extra push buttons for user input.

what schematic program do you guys use? The lcd idea is a great one. I cant believe I didn't think off that.

Digg wrote:what schematic program do you guys use? The lcd idea is a great one. I cant believe I didn't think off that.

A few schematics around this forum are made using EAGLE, its found at this website..

http://www.cadsoft.de/

I highly recommend diptrace - I know alot of people like eagle but I have found diptrace to be the most userfriendly schematic / pcb layout software for sure!

I usually don't do schematics. I usually just place them on DipTrace PCB layout and play with it from there. Although, I have used Visio in the past.

Now thats two for diptrace!

Ok so I have been thinking about this project for a few weeks now and I'm stuck at a crossroads. I started by wanting one board that would allow me to test any circuit that might come to mind.

But not every pic has the same pin layout. I'm planning on using a universal 40 pin zif socket. This allows me to put any DIP in it. So how do you make the board function with the different pics? I was thinking of using ribbon cable to connect the main board to the rest of the board and just crosswire the cable for the different pic designs, there are only a few. Now this is cool as now all I need to do to flip a project to another pic is plug it into the socket and change out the wire.

The next thing that has me is the peripherals that I would have on the board. If I make it as all one board I would not be able to add anything to it after I made it. Also most good PCB programs cost $$$ to do large boards, but the free version lets you do w/e for a smaller board. So what if I broke off each peripheral into its own board? Then if I did that I might as well make all of the the same basic size and shape so they fit together well. Standardizing the boards would work out well because everything could swap places. Just making every board a multiple of a 2x2 or something so that they all fit. The largest chip I know of is the 40pin dip. So make a square that it fits on and everything else can go off of that. The boards can be bigger than this but not smaller. For instance if the main size was 2x2 there could be a 2x4 or 4x6 board. The only restraint would be the places for the screws that would hold them onto the main "holder". That is the part that would need to remain the same.

With the standardized approach I now need a way to connect them. I guess I could go back to the ribbon cable but I'm sure there must be a better way. I'm not really trying to save money with this I just want it to work well when I go to use it. I don't want to have to set up individual jumpers for each wire.

If you guys have any thoughts on this it would be great. Post any ideas or concerns so that I can keep them in mind.

Digg wrote: But not every pic has the same pin layout. I'm planning on using a universal 40 pin zif socket. This allows me to put any DIP in it. So how do you make the board function with the different pics?

You will have to narrow it down to specific chips. There are way too many variations. The cost would be outrageous to do it.

If you still want to do it, then take a look at this: http://www.j1sys.com/pdfs/ICSPAdapters-v1.2.pdf

I purchased my PicKit2 from this guy and he devised a way to use several different chips in the sam ZIF socket by moving pin headers. BUT, that is only dealing with the 5 ICSP pins.

I think using a ZIF socket for the amount of variant microchips available will make it difficult to make a universal PIC board.

Take a look at this Velleman programmer board, it uses several DIL sockets that link up with eachother, but only comes with a 8pin, 14pin, 18pin and 28pin DIL sockets, Im sure that you could add a 40pin DIL socket easily. There is even a schematics on there so you can see how they have connected up the DIL sockets.

http://www.velleman.eu/distributor/supp ... code=K8048

OR: the user manual can be found here

http://www.velleman.eu/downloads/0/illu ... 8_rev4.pdf


The other way would be to use pin headers like these, they make the use of add on boards/daughter boards like AVR and the Amicus18 boards, they use boards that interlink on each other with pin headers. I still think that using some of these pin headers anyway would be good for pluging your LCD into the board etc

Thanks for the quick responses. My first idea was to use multiple sockets but looking a the variety of pics I have at home of the different pin counts I saw that they all had the same basic pins so I was going to go with just one socket with an "adapter". But looking at it some more I just lucked out. I'm now looking at a design that is similar to the PICDEM 2 plus board maid by Microchip http://www.microchip.com/stellent/idcpl ... t=DM163022. It has most of the features that I want but not the way I want it configured. I will make several daughter boards that have the peripherals but keep the ribbon cable design to it just because it will allow me to move the projects without breaking the parts off. I'm thinking of ether using several 40 pin ribbon cable connectors to do the jumping to each daughter board, or just having one and each daughter board would have two and just run it from chip to chip like a bus. I'm Just not sure how many chips I could cross before I started to get too much interference. I may go with a larger cable to add more possibilities to the design if I go with the parallel method. To deal with pics with different pin configurations, I'm thinking of having two headers and two ribbon cable connectors. The ribbon cables would be used or "standard" wiring, and the headers would be used for custom configurations.

I'm still thinking of ways to configure the ribbon cable parallel system. I think I'm going to just standardize the the ports and the internal peripherals that most of the chips have in common; like the 5 ports, the esuart, the spi, usb, and the programmer lines.

So the bus would be something like this:
1. VDD
2-9. Port A
10-17. Port B
18-25. Port C
26-33. Port D
34-37. Port E
38-43. PicKit pins (this will include the second vdd vss on some chips) The rest of the pins will be whatever is needed as they are really just be crossovers from the pins that are already connected through the port pins. But could be used for extra i/o of daughter boards or things like usb.
44-45. TX-RX
46-48. sdi, sdo, sck
49. ...
50. VSS