Hi,
I've taken these shots from the manual of my BOB from Homan Designs in Austrailia. Note the both pins 2-9, the bi-directional capable
and the regular outputs 1,14,16 and 17 are NOT opto coupled. It should be noted that many BoBs do have opto isolated outputs and these diagrams
will not help you if trying to devise a circuit diagram for those types.
It may be that you have non isolated BoB outputs and therefore this discussion may well be of help to you. Another thing to note is that all outputs
have an LED. They are a Godsend when trying to set your machine up especially if new to Mach. If your going to buy another BoB then look for versions
which have LEDs on the outputs and if possible on the input buffers as well like these MB-02V6's.
Another thing to note is that whether these inputs are pulled high or pulled low is determined by a jumper, it adds flexibility but can also create some
confusion, so its a bit of a wash as to whether it useful or not. The important point here is that if say the pull up resistor is engaged high then at idle
the output will be high but with an impedance of 1.2kOhm. A load of only 4.2 mA would drag the output to 0V. If your driver or whatever you
have attached to the output is expecting a current source of more than a couple of mA with the gate idle it will be disappointed and probably fail.
When the output goes low the output will sink around 15mA, the normal sink current of a TTL gate, plenty adequate. When the gate goes high, ie driven
high by its input the gate can source plenty of current, around 20mA. So the situation is that the output is well defined and can either source or sink
current as required and is only marginal if the gate is unpowered, a most unusual condition, a fault really.
Craig