RS-232 (PC) Interfaces for Parallax, Inc. Serial Accessories

Chris Savage

Hello Everyone,
·
·· There have been a lot of requests lately for examples of connecting some of our hardware to PCs or other RS-232 interfaces. ·Most of our serial accessories are TTL level serial and connecting them directly to an RS-232 port can damage them. ·In the interest of helping our customers who wish to connect directly to RS-232 we are providing several example schematics. ·In many cases you can either use a MAX232 line driver IC or simple switching transistors.· There are multiple examples for each interface including some which provide control or feedback to facilitate full control from a PC application such as a Visual BASIC or C++ program. ·These examples will use the DTR line for control and the DSR line for feedback. ·We hope these schematics help you in connecting our serial accessories to your RS-232 serial port.· Every interface/schematic has been fully tested.· Included with each schematic is a complete parts list.· Many of these parts are available from Parallax, Inc.··Some schematics using the MAX232 could be implemented on the Parallax Professional Development Board using the MAX232 IC and DB9 Serial Port connector on it.· Enjoy!
·
NOTE:· We cannot offer additional support for using these schematics.· They are published as is with no warranties implied.· Use them at your own risk.· You should have a good understanding of the·function of the components used in these schematics.·We will continue adding schematics to this thread so while this thread is being populated with the initial information it will be locked.··Take care.

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Chris Savage
Parallax Tech Support


Post Edited (Chris Savage (Parallax)) : 3/26/2007 12:12:24 AM GMT

Chris Savage

RS-232 (PC) to Parallax, Inc. Servo Controller (PSC)
·
Our Parallax Servo Controller (#28023) is typically controlled by one of our microcontrollers. ·For PC control we have a USB version (#28823).· For those who have the Serial version and wish to connect to the RS-232 Serial Port you can use the following schematic. ·It consists of only 5 discrete components which are readily available from Parallax, Inc., Radio Shack or any electronics store or distributor. ·With this schematic you have full control and can even use the PSCI software intended for the USB-PSC. ·Please note that a regulated 5V power supply is required for the circuit which also powers the PSC. ·This supply must be separate from the power supply for the servos, which connects to the screw terminals on the PSC. ·Take care.
·
NOTE: Any data sent to the PSC by the host will be echoed back through the RS-232 connection.· This is a side-effect of using a single I/O pin for bi-directional serial communication.· Be sure your host application disregards anything sent to the PSC.· Essentially you will need to filter what you send from the receive buffer.

PC to PSC.bmp
 
Component  Description         Source          Part #
---------  ---------------     ---------       ------------
R1, R2     1K, 1/4W, 5%        Parallax, Inc.  150-01020
R3         10K, 1/4W, 5%       Parallax, Inc.  150-01030
Q1         NPN, 2N3904, TO-92  Parallax, Inc.  500-00001
Q2         PNP, 2N3906, TO-92  Parallax, Inc.  500-00003

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Chris Savage
Parallax Tech Support


Post Edited (Chris Savage (Parallax)) : 3/24/2007 8:01:37 PM GMT

Chris Savage

RS-232 (PC) to Parallax, Inc. Serial LCD Display (2x16 or 4x20)
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Our Parallax Serial LCD Displays are typically controlled by one of our microcontrollers. ·For those who wish to connect to the RS-232 Serial Port you can use one of the following schematics. ·The first consists of only 3 discrete components which are readily available from Parallax, Inc., Radio Shack or any electronics store or distributor. ·The second uses a MAX232 Line Driver IC.· Be sure to open the serial port on the PC at the baud rate set on the LCD Module. ·Please note that a regulated 5V power supply is required for the circuit which also powers the LCD. ·Take care.

PC to Serial LCD.bmp
 
Component  Description         Source          Part #
---------  ---------------     ---------       ------------
R1         1K, 1/4W, 5%        Parallax, Inc.  150-01020
R2         10K, 1/4W, 5%       Parallax, Inc.  150-01030
Q1         NPN, 2N3904, TO-92  Parallax, Inc.  500-00001

PC to Serial LCD [noparse][[/noparse]MAX232].bmp
 
Component  Description         Source          Part #
---------  ---------------     ---------       ------------
MAX232     Line Driver, 5V     Maxim/TI        MAX232A/MAX232N
C1-C5      1uF, Electrolytic   Parallax, Inc.  201-01050

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Chris Savage
Parallax Tech Support


Post Edited (Chris Savage (Parallax)) : 3/24/2007 7:47:57 PM GMT

Chris Savage

RS-232 (PC) to Parallax, Inc. RFID Reader Module
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Our Parallax RFID Reader Modules are typically controlled by one of our microcontrollers. ·For those who wish to connect to the RS-232 Serial Port you can use one of the following schematics. ·The first consists of only 3 discrete components which are readily available from Parallax, Inc., Radio Shack or any electronics store or distributor. ·The second is a variation on the first allowing the DTR line to control the RFID Reader /ENABLE line and using only 2 additional components. ·The third schematic uses the MAX232 line driver and the fourth uses the same circuit adding control of the /ENABLE line by the DTR signal. ·Be sure to open the serial port on the PC at 2400 bps, 8 data bits, 1 stop bit and no parity (2400, 8, N, 1). ·Please note that a regulated 5V power supply is required for the circuit which also powers the RFID Reader Module. ·Take care.

PC to RFID.bmp
 
Component  Description         Source          Part #
---------  ---------------     ---------       ------------
R1         1K, 1/4W, 5%        Parallax, Inc.  150-01020
R2         10K, 1/4W, 5%       Parallax, Inc.  150-01030
Q1         PNP, 2N3906, TO-92  Parallax, Inc.  500-00003

PC to RFID [noparse][[/noparse]CONTROL].bmp
 
Component  Description         Source          Part #
---------  ---------------     ---------       ------------
R1, R3     1K, 1/4W, 5%        Parallax, Inc.  150-01020
R2         10K, 1/4W, 5%       Parallax, Inc.  150-01030
Q1         PNP, 2N3906, TO-92  Parallax, Inc.  500-00003
Q2         NPN, 2N3904, TO-92  Parallax, Inc.  500-00001

PC to RFID [noparse][[/noparse]MAX232].bmp
 
Component  Description         Source          Part #
---------  ---------------     ---------       ------------
MAX232     Line Driver, 5V     Maxim/TI        MAX232A/MAX232N
C1-C5      1uF, Electrolytic   Parallax, Inc.  201-01050

PC to RFID [noparse][[/noparse]MAX232_ENABLE].bmp
 
Component  Description         Source          Part #
---------  ---------------     ---------       ------------
MAX232     Line Driver, 5V     Maxim/TI        MAX232A/MAX232N
C1-C5      1uF, Electrolytic   Parallax, Inc.  201-01050

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Chris Savage
Parallax Tech Support

Chris Savage

RS-232 (PC) to Parallax, Inc. GPS Module
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Our GPS Modules were designed to be friendlier with microcontrollers which don’t always have the resources to parse the lengthy NMEA strings that come from them. ·This is especially true of the BASIC Stamp.· Using a PC however you can deal with these strings but since the output of the GPS is TTL level serial it is not safe to connect directly to a PC or other RS-232 device. ·The following schematics use the MAX232 line driver IC to connect our GPS Module to an RS-232 serial port. ·The second allows you to control the /RAW line, effectively turning off the data stream when DTR is not active. ·Be sure to open the serial port on the PC at 4800 bps, 8 data bits, 1 stop bit and no parity (4800, 8, N, 1). ·Please note that a regulated 5V power supply is required for the circuit which also powers the GPS Module. ·Take care.
·

PC to GPS [noparse][[/noparse]MAX232].bmp
 
Component  Description         Source          Part #
---------  ---------------     ---------       ------------
MAX232     Line Driver, 5V     Maxim/TI        MAX232A/MAX232N
C1-C5      1uF, Electrolytic   Parallax, Inc.  201-01050

PC to GPS [noparse][[/noparse]MAX232_CONTROL].bmp
 
Component  Description         Source          Part #
---------  ---------------     ---------       ------------
MAX232     Line Driver, 5V     Maxim/TI        MAX232A/MAX232N
C1-C5      1uF, Electrolytic   Parallax, Inc.  201-01050

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Chris Savage
Parallax Tech Support

looyenss

Hello,

I'm trying to program the mlx90614 module with LabView. to use rs232 i want to try the RS-232 (PC) to Parallax, Inc. Servo Controller (PSC) schematic you provided. is it possible to use this one?
i dont want to blow the IR sensor up

Mike G

According to the datasheeet the MLX90614 (Infra Red Thermometer) is an I2C or PWM device. It is not an RS232 device. So you can NOT wire your PC serial port to the MLX90614.

You should use a micocontroller like the STAMP or Propeller to retrieve temperature data from the MLX90614 and forward that data to the via RS232 the PC running LabView.

I2C, PWN, and RS232 are mature technologies information is easily found through an Internet search.

rmoertl

Regarding the circuit for interfacing a PC comm port to the Parallax Serial LCD (including resistors and transistor): The comm port I am trying to connect with is 5V. Will this circuit still work with the existing resistor values of R1=1K and R2=10K? Please advise, thank you!

Chris Savage

These circuits assume a standard RS-232 power with positive and negative voltages. Typically if you just have a positive 5V signal (TTL) then you should be able to connect directly to the LCD unless the signal is inverted.