Newbie needs help with Cheapertronics RFID to Stamp serial connection.
ForceFed
Posts: 5
Hi everyone,
I am using a CheaperTronics.com RFID receiver to read an active RFID tag I got from them also. I have connected the receiver directly to a pc and tested it. It runs at 9600, 8 ,N,1 on hyperterminal with no problems. The only thing that is output from the receiver is a 4 digit alphanumeric code followed by a space. I have connected pin 3 of DB9 from the receiver to pin 2 of my basic stamp 2. Pin 5 from the receiver is connected to Vss on the BOE. I am using a SERIN command to fetch the incoming data
My program will stop when it gets to that command and nothing happens unless I quit manually. The RFID tag outputs it's unique string every 2.5 seconds. I have it active before running the program to make sure it will be visible to the receiver. I even tried reading the tag ID in using a string variable but it never happened that way either. In the stamp manual I saw that you need to use a 22k resistor in series with the input line to the stamp on any input line, but it is not needed on pin 2(reason why I used pin2). Do you think I should use one anyway? Also if the RFID receiver works with my pc then wouldn't I need a max232 to connect to my stamp? Not sure which is which but I think computer logic levels are CMOS and electronics are usually TTL. So I think this means I would need a MAX232 to convert the CMOS signals from the serial out of the RFID to the TTL levels the stamp can accept?
Thanks in advance,
Jared
I am using a CheaperTronics.com RFID receiver to read an active RFID tag I got from them also. I have connected the receiver directly to a pc and tested it. It runs at 9600, 8 ,N,1 on hyperterminal with no problems. The only thing that is output from the receiver is a 4 digit alphanumeric code followed by a space. I have connected pin 3 of DB9 from the receiver to pin 2 of my basic stamp 2. Pin 5 from the receiver is connected to Vss on the BOE. I am using a SERIN command to fetch the incoming data
SERIN 2,84,[noparse][[/noparse]WAIT("23wL")]
My program will stop when it gets to that command and nothing happens unless I quit manually. The RFID tag outputs it's unique string every 2.5 seconds. I have it active before running the program to make sure it will be visible to the receiver. I even tried reading the tag ID in using a string variable but it never happened that way either. In the stamp manual I saw that you need to use a 22k resistor in series with the input line to the stamp on any input line, but it is not needed on pin 2(reason why I used pin2). Do you think I should use one anyway? Also if the RFID receiver works with my pc then wouldn't I need a max232 to connect to my stamp? Not sure which is which but I think computer logic levels are CMOS and electronics are usually TTL. So I think this means I would need a MAX232 to convert the CMOS signals from the serial out of the RFID to the TTL levels the stamp can accept?
Thanks in advance,
Jared
Comments
RS232 normally uses +5 to +8V for one logic level and -5 to -8V for the other. The negative voltages and the higher positive voltages can damage or destroy an I/O pin or the whole Stamp if there's enough current available.
Post Edited (Mike Green) : 7/22/2008 8:12:30 PM GMT
Thanks for pointing that out, I did have it connected to physical pin 2 on my BS2. Going to go pick up a 232 a radio shack and try it out. I have been trying to find current draw for the max232 to calculate voltage drop resistor to drop from 9v to 5v?
jared
The Stamp module has a 5V regulator and, if powered from Vin, will output +5V on the Vdd pin.· There's limited current available there (50mA total).
SERIN 16, 84,[noparse][[/noparse]WAIT("23wL")]This is all of my code other than the DEBUG command afterwards so that I know it worked. Does the Sin pin on the BS2 have an integrated MAX232 or do I still need to wire one in?
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