is this a job for a emitter follower (common collector amp)?

[robismyname]

emitter follower common collector

(history of project)
Im running a serial application using digital radios (TTL devices) where I send data from point A to point B.

On the transmit side I have a microcontroller connected to a transmit radio. The microcontroller connected to the transmit radio generates a repeated string pattern and sends it over the air.

I detect that pattern on the receive side using a receive radio.

I know that I am succesfully receiving the string pattern from the transmitter because I can see the string pattern on my laptop. The laptop is connected to the receive radio with the help of a maxim rs232 ic chip (TTL to RS232 conversion). data sheet of maxim chip attached Im using the chip shown on top of page #17 the max232 not max232A)

(Problem with project)
On the receiver radio, receive data line is going to a maxim rs232 ic pin #11, which allows me to see the string pattern on the laptop monitor. Now I want to connect a microcontroller to the receive radio receive pin as well to do something with the data being received by connecting the microcontroller to pin#11 of the maxin rs232 ic and this is where the problem occurs. When the receiver microcontroller and the maxim rs232 chip are connected to the receive radio receive pin I dont receive data but when there is only the maxim chip connected to the receive radio receive pin I get the data from the transmitter. Why cant I connect both the maxim chip and the microcontroller together? And how do I fix this? Someone told me that I needed a npn emitter follower (common collector amplifier). Well I tried this and it still doesn't work. My design is attached as well

 

[pauloynski]

common collector emitter follower

If you are using a TTL output device then probably the MAX232 will do the job since its input threshold voltage is compatible. However, the input threshold voltage of the CPU may be out of specs. An emitter follower will be of little help in this case. Also, your proposed circuit is AC coupled and will not work. I suggest your using a 74HCTxx (any non inverting type or even two inverters series connected can be used) as a buffer for your signal since it has a threshold that is compatible with TTL. Also, inspecting the signal with an oscilloscope will clear any doubt. Just inspect the high and low level values.

Added after 10 minutes:

If your problem is a low output voltage (something between 2.5 and 3.0 volts when the output is supposed to be "1") then just adding a simple resistor (1k5 to 3k3) from the output to Vcc will do the job.

 

[E-design]

npn emitter follower

Make sure your micro is configured so the port you use as input is actually an input and not an output or something pulling the signal down.

 

[pauloynski]

Re: is this a job for a emitter follower (common collector a

Good guess E-design. Some things are so simple that can be forgotten.