View Full Version : How to start?

Richard Whitaker
07-29-2008, 09:30 PM
Could someone please give me some advice on where to start!?
I would like a small, low-power system to·read-from/write-to·a USB·RFID reader, measure tilt, do some calculations·and output the results to an rs232 serial port (for data logging on a pc) and to a small LCD display.
In a burst of enthusiasm, I bought the following parts…..
BS2P-24 stamp
Super carrier board
Parallax USB to Serial (RS-232) Adaptor (28030)
MAX232 chip (st232cn) with a db9 connector
Hitachi H48C 3-axis accelerometer.
LCD display with serial interface
Then I realised that I have no idea at all of how to connect these things together and program them. Where do I start? How do I find information to show me how to wire the parts together, and is there anywhere where I get some sample PBASIC code for using them? I'm afraid that I have no knowledge of electronics whatsoever......
If anyone can offer some advice, I would be very grateful!
Thank you.
Richard Whitaker

07-30-2008, 01:08 AM
well .. What's a microcontroler is a start to eletronics.


in the botton there's link to download this.

and if you look at parallax documentation of each iten that you bought .. you will find all the examples you need.

Go ease ! each step at once


Richard Whitaker
07-31-2008, 08:45 PM
Amaral - thank you for your help! I've tried to find documentation for these parts on the Parallax site and haven't succeeded - I will follow the link that you suggest. "Whats a Microcontroller" looks like it'll help me a lot.

07-31-2008, 11:39 PM
Most parts that you buy from Parallax have a .pdf guide that you'll find very helpful. Go to the online store, then go to the page for the part (e.g., the accelerometer, the LCD), and look at the documentation. There's usually a demonstration program that will teach you a LOT about how to get that part working with your BS2. For example, on this page you'll find the documentation for that accelerometer:


I strongly suggest that you print out those docs and read them carefully, set up a circuit and run the demo program, and make sure you can get each part doing what it's supposed to do on its own before trying to build your own device. You'll learn a lot in the process, and what you learn will be exactly what you need to learn.

08-01-2008, 09:19 AM
I'm not trying to be a wet blanket or discourage you, but I think you should consider this....

The·Stamp won't be able to interface to the USB device.· There are "co-processor" chips or helper modules·that will let the Stamp talk to a USB thumb drive, but none that I know of that will talk to the USB RFID reader.

You could connect the USB RFID reader to a computer and program the computer to send information to the Stamp for processing.· Or, you could change RFID devices, something like Parallax's, which could be interfaced to the Stamp.

Most importantly, get started!· The Stamp will teach you a lot, such as how to wire and talk to each device, how to interface them together and what kinds of data you get back from each device.· Break your project down into simple steps, get that·step working, then work on the next part.

Just be aware that long term, to meet your goals, you may need to change processors, to something·like the Propeller or SX.

Mike Green
08-01-2008, 10:24 AM
Depending on how the USB RFID reader is set up, the Parallax USB Memory Stick Datalogger may be able to talk to it. This is sold primarily for its ability to interface a USB Memory Stick to a Stamp or Propeller or what not, but it can handle most devices that look like a keyboard or mouse or other HID (Human Interface Device). There's no ready-made sample code as there is for a USB Memory Stick, but you might have a look at the Vinculum chip Firmware Manual which does most of the work for the Datalogger. There's a link for this on the Parallax web store product page.

Richard Whitaker
08-02-2008, 12:05 PM
Hi, thanks for the ideas.
I currently have the (Tagsense active usb) rfid reader connected to my laptop usb port and I control it with vb.net code. The code sends string commands to the tags via the reader, which changes their mode of data reporting. The reader receives their reports and feed them back to the laptop. I want to measure the tilt of the board/laptop, combine that with some time data and write strings back to the tags. The reader takes power from the usb cable from the laptop. I need to get rid of the laptop for portability and I need to add an inclinometer.
Are you saying this is not possible with the stamp and a MAX232 chip (st232cn) with a db9 connector with a serial-usb converterParallax USB to Serial (RS-232) Adaptor (28030)? Because I won't be able to read and write to the port or because it won't power the reader through the port?

Mike Green
08-02-2008, 12:39 PM
The Parallax USB to Serial adapter is a USB client. As such, it requires a USB host to control the USB communications. The Tagsense RFID reader is also a USB client and requires a USB host. The PC functions as a USB host. You need something to take the place of the PC. The Parallax USB Memory Stick Datalogger functions as a USB host for the USB Memory Stick. Like I said, it has the capability of functioning as a USB host for several other types of devices including most USB keyboards and some USB To Serial Adapters. It might be able to host your RFID reader, but it's impossible to tell without more information. The USB Memory Stick Datalogger does furnish +5V up to 100mA as required of USB hosts.
Note that this uses the FTDI Vinculum USB host chip. FTDI also makes their own host devices using their own chip. There's no particular advantage of either other than that Parallax supports their own version while you have to go to FTDI for support of theirs. I've used the VMusic2 which is a USB host with an MP3 decoder. It works well, comes in a nice little plastic case.