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is my intercom/telephone/sounder/strobe circuit between shop and garage. It utilizes an assembled part (P1) on the schematic,
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The shop has machinery that needs a loud bell and a strobe when the phone rings. It also needs these to get attention for intercom paging. This is needed from the house to the shop and from the shop to the house.
I haven't built the thing yet. All the materials are expensive.
Notice that the intercom is made up of 2 wired phones with one of the phone wires cut and a 9v battery and 200 ohm resistor inserted in series with it. This makes for a cheap intercom but it also needs an alarm to alert the other end that it needs to talk.