Ok, before I get too far, I am reasonably a newbie (everyone panic). However, I do have some experience in C++and Z80 asembely (ok I can get an led to blink).
So, what I want to do is make a wireless link for a ti-83+ (texas instruments graphing calculator running on the Z80 processor). This link will connect into an already exsisting I/O port and the information from that I/O port will be transmitted without any change to the data.
I was wondering what parts I would needin addition to the RF Link - 2400bps. Also, It wont need any kind of screen or interface other than possibly a switch and a led that signals it is sending or recieveing.
Thanks
p.s. before you ask, my dog’s name is Sparky, nothing to do with Sparkfun and I had an idea a while back that I never went through with which is why my date that I joined is old.
The problem with the 2400bps RF signals is that they will not automatically retransmit bad data or check for bad data. This isn’t as much of an issue for a wired connection. Also, you’d need a preamble (think of it as knocking) to get the system to recognize that good data is coming in vs just random noise. Even with a good reamble and CRC and a way to determine good from bad, the data can still be corrupted and need to be transmitted.
So, if you’re willing and ready to write a TX and an RX program for two microcontrollers to act as the intermediary, you’re good to go. I think you’re going to need that regardless actually, since you want the link to be transparent. Also, what is the actual baud rate of your data port? If it’s 2400bps, you’re not going to get all the data transmitted due to the above data loss issues and overhead.’
Unfortunately, this is reality. However, there are other options beyond the 2400bps radios. What range are you looking for?
Depends on the Bluetooth class. I haven’t really looked at it since before they released the newer revisions (particularly 2.0). Class 2 is 10m, class 1 (I think, or is it Class 3?) is 100m.
I have not done a BT setup with the Sparkfun modules. However, Bluetooth setup is supposedly very simple. You have to issue a few “AT” modem commands at first to configure the module and connect, but after that it’s supposedly transparent.
you are going to have to design a reliable transport. use error checking and retransmit to get good reliability. this will add a fair amount of overhead so while the connection to the device will run at 2400 baud, you will want to transmit at a higher rate. you will also need to buffer data from the calculator so you can retransmit…
take a look at the data from the calculator. it must have some sort of structure you can exploit to increase reliability and performance. you might also be able to do compression to decrease the number of bits transmitted. think packets - the larger your packets, the lower your overhead.
Samnsparky:
So, what I want to do is make a wireless link for a ti-83+ (texas instruments graphing calculator running on the Z80 processor). This link will connect into an already exsisting I/O port and the information from that I/O port will be transmitted without any change to the data.
The easiest way is to purchase a pair of wireless serial port extenders. Lots of these on the market. They accept a DB9 RS232 connection at each end and make it transparent - sending and receiving. Usually at 50-250Kbps.
Don’t know what your cost goal is but these are pretty expensive, like $175 each or so. Sometimes see older used ones on eBay for a lot less.
Less plug and play - I’d say the least expensive but still easy way is to use a pair of IEEE 802.15.4 modules. There is a ZigBee network protocol for these, but it’s not needed for simple networks. MaxStream (now Digi) makes the XBee modules. $20 each. Just connect to the serial port of the module with 3.5 volt serial data (you may have to level shift and get the data inversion correct). Use a PC and terminal program to configure each module once - telling it the baud rates and the MAC address of its mate. Same module in a box with RS232 or USB drivers is $109.
No protocol software at all to develop.
Taking a $5 transmitter and a $5 receiver and developing all your own bit/byte/frame protocol code and error correction would be a learning experience, but an advanced project.
IEEE 802.15.4 modules - not chips - (there are several vendors) is much easier and cheaper than Bluetooth, IMO.
I am sorry about not being near my computer in a while I had just too much to do yesterday. I will look into the wireless serial port extenders and some of the various other ideas. Thankyou for your help.