Pic to Pic - serial distance

[Wp100]

Hi,

Have an existing 10 mtr run of Cat 5 cable and want to send data from one Pic18F to the other, just a couple of bytes every minute in one direction only.

Can I do it reliably at 5v without a level converter like rs232 ?

thanks.

 

[MikeMl]

Depends entirely on the RFI and EMI environment. Another problem is that you are likely to have a different ground potential 100 feet apart.

Direct connection not recommended. I would use opto-isolation or transformer-coupling.

 

[Mr RB]

5 v data comms over 10 metres of twisted pair shielded cable should be fine. Use a real low data rate like 1200 or 2400 baud and you can even use an RC filter on the receiving end as the PIC USART input is a schmidt trigger input and is very tolerant of a data signal that has a slight ramp on edges.

I've had success with 19200 baud and 5v comms over shielded cable of longer runs than that, but like Mike says it's always dependent on noise pickup and possibly ground levels.

 

[be80be]

He shouldn't have a thing to worry about there will be almost no voltage lost

The balanced signal twisted pairs helps preserve a high signal-to-noise ratio despite interference from both external sources but don't try high baud rates.

Transmission of a signal over a balanced line reduces the influence of noise or interference due to external stray electric fields. Any external signal sources tend to induce only a common mode signal on the line and the balanced impedances to ground minimizes differential pickup due to stray electric fields. The conductors are sometimes twisted together to ensure that each conductor is equally exposed to any external magnetic fields that could induce unwanted noise.

Some balanced lines also have electromagnetic shielding to reduce the amount of noise introduced.

A balanced line allows a differential receiver to reduce the noise on a connection by rejecting common-mode interference. The lines have the same impedance to ground, so the interfering fields or currents induce the same voltage in both wires. Since the receiver responds only to the difference between the wires, it is not influenced by the induced noise voltage. If twisted pair becomes unbalanced, for example due to insulation failure, noise will be induced. Examples of twisted pairs include Cat-3 Ethernet cables or telephone wires.

Compared to unbalanced circuits, balanced lines reduce the amount of noise per distance, allowing a longer cable run to be practical. This is because electromagnetic interference will affect both signals the same way. Similarities between the two signals are automatically removed at the end of the transmission path when one signal is subtracted from the other

I guess there is a chance you could get more then you put in the wire back out at the receiving end .

 

[ericgibbs]

Hi,

Have an existing 10 mtr run of Cat 5 cable and want to send data from one Pic18F to the other, just a couple of bytes every minute in one direction only.

Can I do it reliably at 5v without a level converter like rs232 ?

thanks.

hi Wp,
For a 10mtr [33ft] run in a Cat5 cable you should have no problems up to 9600 Baud.
If you have any spare wires within the cable connect them all to 0V at both ends of the cable.

 

[Wp100]

Hi,

Thanks guys, as I only need teletype speed sounds like it should work ok, can easily use a simple checksum to ensure data intergrity.