Root/labsw/README

Source at commit b64d4673d8dc291f783b6459c010705519cb052b created 5 years 5 months ago.
By Werner Almesberger, ircstat/mlstat: change "milkymist" label to "m-labs"
1Opto-isolated inputs
2--------------------
3
4The C8051F320 needs a current of at least 50 uA to drive an input low.
5The current transfer ratio of the opto coupler is 50% or better.
6Thus we need an input current of at least 100 uA.
7
8If we allow for a loss of at least 100 mV (yielding a minimum input
9voltage of 1.5 V), the protection resistor can be at most 1 kOhm.
10
11If the maximum power dissipation of the protection resistor is
12limited to 1 W, we can allow up to 30 mA into 1 kOhm +/- 10%.
13
14The maximum input voltage would thus be 30 V.
15
16
17Future changes for higher voltages
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19
20The circuit is currently not designed for voltages exceeding about
2130 V between any two points !
22
23To allow the use with mains voltages, be it across the relays or be
24it as a difference in "ground" potential of separate loops, at least
25the following changes will be necessary:
26
27- air gaps must be 2 mm or larger (6 kV)
28- conducting elements closer than 2 mm must be isolated if high
29  voltage may exist between them
30
31In particular, this means:
32
33- the PCB must be coated
34- opto couplers may not share the same socket
35- the opto coupler headers (inputs and outputs) need wider spacing
36- clearances need to be verified
37

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