mirror of
git://projects.qi-hardware.com/wernermisc.git
synced 2024-11-15 09:16:14 +02:00
37 lines
1.2 KiB
Plaintext
37 lines
1.2 KiB
Plaintext
Opto-isolated inputs
|
|
--------------------
|
|
|
|
The C8051F320 needs a current of at least 50 uA to drive an input low.
|
|
The current transfer ratio of the opto coupler is 50% or better.
|
|
Thus we need an input current of at least 100 uA.
|
|
|
|
If we allow for a loss of at least 100 mV (yielding a minimum input
|
|
voltage of 1.5 V), the protection resistor can be at most 1 kOhm.
|
|
|
|
If the maximum power dissipation of the protection resistor is
|
|
limited to 1 W, we can allow up to 30 mA into 1 kOhm +/- 10%.
|
|
|
|
The maximum input voltage would thus be 30 V.
|
|
|
|
|
|
Future changes for higher voltages
|
|
----------------------------------
|
|
|
|
The circuit is currently not designed for voltages exceeding about
|
|
30 V between any two points !
|
|
|
|
To allow the use with mains voltages, be it across the relays or be
|
|
it as a difference in "ground" potential of separate loops, at least
|
|
the following changes will be necessary:
|
|
|
|
- air gaps must be 2 mm or larger (6 kV)
|
|
- conducting elements closer than 2 mm must be isolated if high
|
|
voltage may exist between them
|
|
|
|
In particular, this means:
|
|
|
|
- the PCB must be coated
|
|
- opto couplers may not share the same socket
|
|
- the opto coupler headers (inputs and outputs) need wider spacing
|
|
- clearances need to be verified
|