Let's Make Robots!

New Project Board

hmm didnt read wihle writing this, its rather long. Skip to the bold to see my questions


Alrighty well i know you guys havent seen it but i did end up finishing the start here bot and it works... cept it has no wheels. Obviously it wouldnt be very intreasting to post a video of that so when i do end up making another order from solarbotics ill be sure to pick up the wheels (hopefully soon, youll see).

I've been screwing around with the arduino for the past two weeks and although the nicest feature for me was that the power came from the USB cable by far the most convinient thing to happen since i started robotics, the programming itself seemed so much more overly complicated that Basic. I'm assuming you can do more but i figure ill leave some challenges for later. So now... with the release of the X2 line ill be switching back to pic controllers, and the first thing i want to do is build my own board. 

I've been looking forward to this for a while actually, custom project boards have always intreated me (the generic look, and it makes you look smarter). Also half the fun of robotics IMO is building the bot (if not all). Since i've joined  a couple months ago im starting to get a much better idea of how custom boards work. After moving my 28x1 to a breadboard and then running my LED sketch, i felt i was going in the right direction. Im on the verge of placing an order for two 40x2's and two 28x2's (just in case i fry one... or two.. or three...) theres also no point in placing multiple small orders, ill just order them all at once :).

Idealy i would want to start off building a 28x2 "project board" as a custom build moving up to the 40x2. To make things easier i want to include the USB port thingy somewhere which i know uses three wires on three pins. i've turned to almost all other sources i had acess to about building custom boards and none helped. I read the manuals and they gave me some nonesense telling me to buy more chips so i could make my own board, not actually how to make it.

This post is mostly about creating a ground or base of knowledge to start the board. I have some really seemingly stupid questions to ask but i wouldnt know how to search them. 

On the 28x1 project board, each IC pin goes to a set or more of 2 pins with the option of a third. i know that one is the signal pin/ output another is 5v and the one you solder in is ground. going off what a servo requires. it would be easy to look at the data sheet and determine which pins are outputs, ground, or 5V. i know very little about circuits and schematics, but could you theoretically connect all the 5V's? And would that supply equal power to all of them?

 Secondly, there all these resistors, a capacitor, i think the blue thing is a cap, as is the long black rectangle. And a little square thingy. How would these be wired up to the chip?

I also want to add an l293D or another motor driver and i saw guibots tutorial (http://letsmakerobots.com/node/2074) however that looked a bit to complicated. 

If i can build a board with that expansion in mind, i will be more than pleased. Also if im getting too far ahead of myself please let me know.

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Despite the title, I'm not going to say that you DON'T need the resonator or cap, but ...

I've built a few boards of my own for the picaxe 28x1 using only the following components:

-22k and 10k resistor for the download

-10k pull-down resistor for each digital input that you're using.

-4k7 pull-up resitor for the axe

header pins.

The datasheet for the project board has a complete schematic of how the board works, minus the motor driver. But that's also easy to slap on there as well.

right, my mistake, the 28x1 has an internal resonator.

I strongly reccomend the reset button, saves some headaches. You might also want to put some male header soldered to the serial pins so that you can connect them to another (small) board with a few resistors and the 3.5mm jack socket. This way you can download the program to your MCU without having to take it off every time from its holder. 

first, thanks robologist, that second link was very helpful, also i have the pic USB cable which i believe has the TTL to rs 232 converter inside it. Secondly thanks Tuna, that would make things much easier to wire. Ill have to stop by a radio shack to check for parts this weekend.

practice says you don't have to tie to ground via the resistor every input pin, but only the ones you are using.

Another thing: if you can't find the 3 pin resonator you can also get a standard two pin crystal and connect each pin to the ground via a 22pF resistor (one per leg). Well of course you'll also have to connect each pin to the resonator pins on the MCU. 

Frits has a very nice write-up about the project board here. The blue thing looks like the 4 MHz resonator, serves as the clock the PICAxe runs on. Long black rectangle is probably the SIP resistor, a series of 8 resistors in a package to be a pull-down to some of the PICAxe pins. The schematic for how things are connected the board is here, on page 2. It discusses adding a motor driver in the lower socket on page 4. All things wired together would have the same potential, so all +5 volt pins would be +5 (unless too much of a load was connected).

Also, USB uses 4 pins, +5v, ground, Data+, Data-. A translator chip is needed to take the USB serial data and translate it to the TTL level serial needed by micros. Check the FTDI website for some simple solutions.