http://www.nkcelectronics.com/RS232-to-TTL-converter-board-DTE-with-Male-DB9-33V-to-5V_p_369.html(There several photos and also a schematic for the product shown at the link above).
I have one of the above RS232 to TTL converters.
I'm simply trying to get the RS232 voltage to drop down to the TTL range, but something is amiss
I have connected two of the male pins on the TTL converter's RS232 connector to a RS232 port on my PC. Using HyperTerminal I can cause the green (RX) LED on the converter to blilnk. Each key press on the PC causes one green blink. By moving the wire from the PC port to the TTL converter one pin further over on the converter I can also make the red (TX) LED blink. (In this case it makes a "soft" red blink.)
The LEDs are clearly being powered by the RS232 port as there is no other power being applied to the converter (at this point in the process).
I have added header pins to the side of the TTL converter that is opposite the RS232 connector. When I attempt to read any voltage on the header pin side I get nothing. (I have probed GND and RX and GND and TX.)
In reading the literature for the product I figured that the coverter chip might need some voltage beyond what it gets from the RS232 signal coming from the PC. I can't really figure out why this would be the case except that the converter board has a pin called VCC - so I tried adding 3V (and also 5V) from my power supply by connecting the power supply to the VCC and the GND pins header pins. With voltage from the power supply applied to the converter board the red TX LED turns on continuously and brightly. While this is occuring I can hit keys on the keyboard and get the green RX LED to blink.
If at this point I move the PC's RS232 port power wire (the non GND wire) to the converter's top middle pin (which normally powers the red TX LED), the bright state of the red LED goes off, but the soft red blink ability of the red LED works as I hit keys on the keyboard.
What I would have expected from all of this is that I should have been able to probe the header pins on the coverter (with my scope or a DMM) and see voltages between 0 and 3V or between 0 and 5V as I depress keys.
The goal was to see the higher voltage from the PC RS232 port come down to the TTL range, but so far no luck.
Any suggestions? Thanks!