I think you’ve got something here… 
Yes, indeed, and I think even I might be able to do something like that. You could make all sorts of interesting modules to add to this. Using the Bluetooth 2.0 dip package from Sparkfun, it would be really easy to add Bluetooth.
8-Dale
The “about 1V” is probably the random output when the rcvr is not receiving anything.
I just did some checking on the bench, and noticed these things (note that I did this with the 4800 baud version at 434 Mhz, I don’t know if yours would be different):
On the xmtr, when the data line is low (0V), it is the same as when the xmtr is not powered up at all - there is no output. When the data line is high, there is a constant output (verified with an oscilloscope). So there is nothing unexpected about how the xmtr works.
On the rcvr, when it receives a constant signal (xmtr is on), the data output initially goes high, but only temporarily! After about 1/4 of a second, the output goes low and stays low. There is no random noise as long as the xmtr stays on. This means that it would NOT be possible to use a super-slow baud rate (not that you would want to anyway).
As long as the xmtr output cycles on and off at least a few times a second, the rcvr output follows the xmtr input.
SO, since you have changed the freq adjustment on your rcvr, and it may be wrong, I’d suggest the following experiment:
Power up the xmtr, and connect the Data line to +5 continuously.
Monitor the output of the rcvr. I assume it will be at the “about 1V” level as you mentioned. Slowly adjust the rcvr until the output goes to either 0V or 5V.
If possible, physically separate the xmtr and rcvr by several feet (or more), and repeat the adjustment to find the best setting.
It is unclear to me what the difference is between pin 2 and pin 3 on the rcvr. The output signals look basically the same.
Using only the rcvr and my oscilloscope, I connected the rcvr’s antenna to a long wire (a shortwave radio antenna, which goes up to the roof of the house). Every few seconds I could see a ‘signal’ at the rcvr output (a quick string of pulses, not random noise). It is probably the transmissions of garage-door openers and other gadgets being used in the neighborhood.
Pete
For the ‘transceiver’ module, I plan to set up the TLP-434A type modules with a xmtr and rcvr that share a common antenna, running half-duplex on the same frequency.
I have a design (only on paper) that does T/R switching using a pair of PIN diodes, an inductor, a couple of C’s, and a couple of R’s. A PIC will be available to do the T/R switching, so it’s not necessary for it to be ‘automatic’.
Has anyone tried anything similar?
Is there a simpler way that is effective?
Given that the xmtr is rather low-power, is there any danger of damaging the front end of the rcvr?
Pete
Pete,
Ive got my tx and rx setup in front of me right now. I have 5V going to the input line of the tx and the rx hooked up accordingly.
I turned the adjustment while monitoring the output with a volt meter. It seems to always be around 1V no matter where the screw is positioned. I cannot get it to go to 0 or 5V at all.
I have 2 sets of these modules though, 1 I adjusted and 1 straight from sparkfun and they both look the same on the voltmeter.
BotHakr,
I guess I don’t have any other ideas, except to use some better test equipment to figure out what’s going on…
Pete
Me being a biped fan, I would love to see a board dedicated to ballance control. Like the Honda ASIMO, if pushed, the motors work against the force keeping it stable. I know there are gyros and tilt sensors, but a “smart board” that can adapt would be nice.
Answering my own question on how to best do this:
A fellow in the SparkFun forum pointed out an SA620 chip which does exactly what I need… It’s an SOIC-8 package.
Pete
That’s a good idea Mike - a “positional sensor” board or whatever, that stacks on top of the CPU board.
My initial set of boards will be the following 3 boards, which will use up an ExpressPCB “miniboard”:
Pete
Ok I am getting closer!
Just for kicks I decided to hook pin 3 of the rx up to my serial port instead of pin 2. When I reset the pic setup to transmit I can see the character show up on the terminal…but only right after I reset it. It seems to be transmitting pretty good other than it only transmitting 1 character (by the way, changed it to only transmit all “hhhhhhhh” instead of hellohello…).
The walkthrough states that pin 3 on the rx is the “linear output”.
This is going to be very cool. I like your idea!
I’ve been moving forward on this project lately. The schematics are at:
www.geocities.com/saipan59/robots/stackable.zip
Each of the 3 schematic pages is a separate module, but all 3 of them are being layed out on a single board. When I get the PCBs, I’ll cut them apart.
I went with an 18F2620 on the MPU board, because it’s about the most functionality I can get in an SOIC-28 package. Nearly all the components are surface-mount.
The boards will be ‘stackable’, such that the MPU is always on the bottom, and I can plug either of the other boards on top of it (no cabling).
The FET board includes one H-bridge (up to about 4A capacity), plus 6 other switched signals (2 hi-side, 2 lo-side, and 2 that will either source or sink).
Pete
I just ordered 3 PCBs for this project. They’ll probably not get here until Tuesday the 2nd, due to the holidays.
All the files latest are here:
www.geocities.com/saipan59/robots/stackable.zip
The zip file is about 300 KB.
On the MPU portion, I added a spot for a 32.768 Khz crystal, for doing “real-time clock” stuff.
On the radio transceiver portion, I added a comparator circuit to the rcvr output, although I don’t expect to need it with the modules I have now.
Pete
The boards came today!
Here are two pix:
www.geocities.com/saipan59/robots/bare.jpg
www.geocities.com/saipan59/robots/mpu_stuffed.jpg
Everything works so far - I put some code in to blink the LED…
And, my first attempt at surface-mount soldering seems to have worked.
Pete
Very nice, Pete!
That bugger sure is tiny.
I certaintly agree about the 2620’s.
Microchip seems to have had an eye towards real-world control in a tiny package.
In fact, I’m writing code (in assembly 
) right now for one that I plan to stick on a 6DOF biped.
That “positional sensor” board sounds interesting.
Dan Albert was making a 6-axis IMU board small enough to fit in his Nova, but that bum up and moved to CA before I could “borrow” it from him.
I have been poking around for a while, now, but I still haven’t found gyros cheap enough to warrant making a board for them.
The necessary accelerometers are in my price range, though.
All 3 modules are assembled now. I’ve tested the MPU and transceiver modules, and didn’t find any HW problems. I’ve got some basic code working that uses the xcvr - it receives a packet of data (from a similar device), waits 1 second, then sends the same data back (so it’s half-duplex). I think the next batch of modules will include one that has various sensors on it, such as temperature, light, sound, etc.
I’m enjoying the SMT thing, since I can cram so much stuff in a small space.
The power/motor control module is still untested.
Pete
Here’s a pic of all 3 modules:
http://www.geocities.com/saipan59/robots/stack1.jpg
And here’s what they look like plugged into each other:
http://www.geocities.com/saipan59/robots/stack2.jpg
Pete
thats very professional. I can see you have good soldering techniques! Well done. Thats awsome!
Very cool Pete!
This makes me want to design another board also. I have not been around lately but I do miss the hobby. Problem is I’m in to everything these days. I have been busy going to the gun range and punching lead through paper. 
Have you looked at the propeller? That would be a nice chip to put on a project board. Powerful multi-tasking and real time processing.
We’ve missed you Mike
