Best way to prototype hardware with PIC

[Guest]

HI Everyone,

I have a PICDEM 2+ demo board, and using that, I have finished most of the software for a project, but now I want to really focus on creating the hardware.

I started using a breadboard, and i got it to work, but for some reason, I think the connections with the crystal (32K) or decoupling caps (~20 pF) arent working well. I think its because the breadboard isnt great for this application because of the 32K crystal. For the compiler I have the clock set up as XT. Should I be using the HS option?

Also, should I be using different capacitors with that crystal (how can I calculate what capacitor I should use versus the clock speed?). Also, have people used breadboards to prototype with clock speeds in the MHZ range? If so, what should I be aware of?

If using a breadboard to do hardware prototyping isnt feasible, what should I use? I'm hesitant go get a PCB made and then find out it doesnt work. What's the best way to do hardware prototyping for microcontrollers?

Thanks!

[rwyoung]

What kind of breadboard are you using? If it is one of the white plastic kind where you push in little wires, then your crystal circuit may never quite work right.

There are application notes (from Microchip and from crystal manufacturers) detailing the proper selection of components as well as how to construct the circuit. Guard rings and short ground runs are important.

Having circuit boards made is relatively inexpensive compaired to the headaches and what your time is worth when dealing with dodgy breadboards. At the very least, consider getting the perforated board with solid copper on the top and bottom. You use a little tool to isolate the holes. Gives you something close to solid power and ground planes for a prototype. Or learn how to etch your own circuit boards.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month!

[Humberto]

[treitmey]

I don't want to complicate things... but to solve the breadboard/crystal problem you could chose a PIC with an internal OSC. Then the beadboard
may work great for a prototype. I always look for the easy way out.

[rnielsen]

I, usually, build my proto-types on a breadboard first so I can make changes as needed. Once I get things running there I'll etch a PCBoard and put things together to ensure that the hardware is solid. If you go to www.pulsar.gs they have items there that will help you make a fairly inexpensive board and it doesn't take much time. Simply download a schematic/PCB program (there are several threads on this board about them) and you'll be in the PCB business in no time.

Ronald

[newguy]

I have a Micro Engineering Labs Lab-X1 board (http://www.melabs.com). It has a variable clock oscillator on board, settable with jumpers. It also comes with spaces for you to install pin headers/sockets for making easy direct connections from the PIC to external hardware.

What I do is prototype external circuitry on one of those white solderless breadboards, and make connections from that to my PIC.

[iso9001]

I've used that white breadboard type for some of my projects and have never had a problem yet. Thats usually with 10Mhz resonators with built in caps, however....

I have found that through some magical bread board properties I can take a 20Mhz fox can-type xtal, plug it into the breadboard with no caps and it works fine. I know its by sheer luck that it works. I don't even want to look at that setup on the scope. It would give me bad dreams.

I'd agree with the internal clock for now. Then when you make the pcb, give yourself some options. Like for the first couple pcb's I made since I didn't know what was going to work and what wouldn't, I made two spots for different xtals, different cap options, spots for pull ups/downs etc etc. I still do that with new circuits now and then.

[newguy]

[jbmiller]

I've used the white breadboards since the 16C84 came out(ugh,that's been a while!) and on the 20MHz 16F877s.Never had a problem and I use 20GA soild copper wire(Bell tell 6 pair) for jumpers.Then I 'solderstitch' the circuit onto Ratshack perfboards(4 by 6" size),again no problems. Either I'm lucky or my neat and tidy approach is good.
Jay

[PCM programmer]

[newguy]

[Stu_H]

I always use the white plastic breadboards to get a project started. I've not had any major problems so far, and I've been doing it this way for over 10 years. PIC12/16/18 series, all work fine. I usually use a crystal oscillator for projects with a single PIC, and with the 18F series I've found that even the HSPLL at 32MHz works fine on the breadboard.
Of course, I'm lazy. I omit the 22(ish)pf capacitors that should be on each leg of the crystal to ground when using a breadboard - just stuff the crystal across the appropriate pins. (I do it properly on the PCB!)

Stray capacitance on the board making things OK? I don't know, all I know is that it works - even with the 18F PICs at 4x PLL!

(I *have* been using the same plastic breadboard over that time - perhaps others might not be so tolerant).

[sd211]