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STD Controlled Outlet

License: MIT

Mode: Editors' pick

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Update time: 2023-03-11 17:34:42
Creation time: 2021-04-21 05:56:16

Using a house fire alarm to shut-off a power outlet. The circuit uses transistors in a latching fashion, such that anything can happen to the fire alarm, it can stop or burn, the circuit will remain latched and the power outlet will not be conducting. Until the user comes and reset the unit. The circuit uses a photo-isolator between the fire alarm and the circuit, 4 transistors and a 16A relay for the power outlet. The photo-isolator allows an alarm unit to provide a trigger at a voltage up to 30V and also ensures that a voltage spike from the fire alarm will not cause further harm to the circuit, in case the fire alarm short circuits or burns for example.


Jumpers JP1A and JP2B are available in case external indicators already contain their needed resistors. In such case, the jumper should be shorted.

Jumper JP3 is available in case another relay is used. Shorting JP3 will provide the full 12V at the relay bobbin. Keeping JP3 opened provides a voltage of ~9V at the relay bobbin and keeps the power dissipation at a minimum; since the relay is meant to be activated during normal operation.


In addition to the surface mounts components listed in the BOM, the project needs these through-hole components:

1 Relay: RZ03-1A4-D012 (works up to 264VAC 16A)

1 AC/DC Transformer: RAC03-12SK (produces 12VDC, accepts AC up to 264VAC)

1 "TE Connectivity" Male connector for the fire alarm, part number: 643488-1 (digikey: A25429-ND)

2 Terminals for the optional external indicators 3.5mm pitch, for example digikey 609-4725-ND

3 Terminals for high voltage wires, the PCB works with "Metz Connect": 360381 (digikey: 1849-1248-ND, will work up to 16A)

Note: The female counterpart connector for the fire alarm would be 1-480303-2 (digikey: A121323-ND) along with 3 contact sockets 61117-4 (digikey: A100716CT-ND)


3D CAD on grabcad

Fire alarm need to be a "hardwired" type (meaning not battery operated) with an interconnect. I used the "First Alert" model BRK-9120B


Video in action

Purchase assembled on Tindie

Design Drawing
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ID Name Designator Footprint Quantity BOM_Supplier BOM_Manufacturer BOM_Manufacturer Part BOM_Supplier Part
1 220uF C1 CAP-SMD_BD8.0-L8.3-W8.3-FD 1 LCSC LELON VZH221M1CTR-0806L C134517
2 1uF C2 C0603 1 LCSC SAMSUNG CL10A105KA8NNNC C5673
3 SM4007PL D1,D2 SOD-123F_L2.8-W1.8-LS3.7-RD 2 LCSC MDD SM4007PL C64898
4 Yellow LED1 LED0603-R-RD 1 LCSC EVERLIGHT 19-213/Y2C-CQ2R2L/3T(CY) C72038
5 Green LED2 LED0603-R-RD 1 LCSC EVERLIGHT 19-217/GHC-YR1S2/3T C72043
6 MMBT4401 Q1,Q2,Q3,Q4 SOT-23-3_L2.9-W1.3-P1.90-LS2.4-BR 4 LCSC SEMTECH MMBT4401 C83940
7 750 R1 R1206 1 LCSC UniOhm 1206W4F7500T5E C17985
8 10K R2 R0603 1 LCSC UniOhm 0603WAF1002T5E C25804
9 47K R3,R5,R6 R0402 3 LCSC UniOhm 0402WGF4702TCE C25792
10 5.1K R4 R0603 1 LCSC UniOhm 0603WAF5101T5E C23186
11 2.1K R7,R8 R1206 2 LCSC BOURNS CR1206-FX-2101ELF C204745
12 560 R9,R10 R0603 2 LCSC UniOhm 0603WAF5600T5E C23204
13 2.7K R11,R12 R0603 2 LCSC UniOhm 0603WAF2701T5E C13167
14 10 R13 R1206 1 LCSC UniOhm 1206W4F100JT5E C17903
15 MOCD213R2M U1 SO-8_L4.9-W3.9-P1.27-LS5.9-BL 1 LCSC ON Semicon MOCD213R2M C258244


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