How are relays driven from the Remote Port?
The remote port outputs are TTL compatible and protected with 1kohm series resistors.
This means that less than 0.5mA can be reliably sourced from these outputs.
The 5V supply (pin5) is protected with a 75ohm resistor so less then 10mA should be drawn to avoid excessive voltage drop.
To drive relays from the remote port outputs, buffer of some type is required.
A common example of a buffer IC is the Motorola MC14049:
This consists of six buffers. The remote port will comfortably drive the inputs of these buffers. The outputs will source 20mA or more, but will more reliably sink current of 70mA or more.
The chip can be powered at up to 18V, thus the AT3600 USER port power may be used. (The remote port power is also limited).
To make the most of the AT3600's available power and the IC's sink ability connect in the following way:
Take the required remote port output and pass it thro 2 buffers in series.
e.g. REMOTE pin 2 (PASS) to pin 3 of the IC. Connect pin 2 to pin 5.
Now pin 4 is a buffered duplicate of remote port pin 2.
Supply the IC pin 1 with +12V from the USER port pin 5.
Common OV: REMOTE port pins 7 and 8 connected to IC pin 8.
Connect a 12V relay (min coil resistance say 150Ohm) between IC pin 4 and +12V
Fit diode protection across the relay as normal. (Cathode to +12V)
Please find the attachment “Remote port D type connections”
Please find attachment for the “Motorola MC14049”