uSDC20D micro Shutdown Controller 
automotive micro-computer controlled PC power sequencing device



  • Startup/Shutdown Motherboard On/Off Pulse

  • 20-Amp Load Switch

  • Voltage Sensing of Battery to prevent over discharge

  • Adjustable Low Voltage Threshold

  • Adjustable Power Down Timer Control

  • Optional Startup on "Engine Running"

  • Temperature Sensing (Environmental Protection)

  • Very Low Standby Power (50 micro-Amps Typical)

  • State indicator feedback LED (Flashes at different

  • Microprocessor Control

  • Fuse Protection (20-Amp mini-fuse)

  • Reverse Voltage Protection

  • Load Dump Protection (Over Voltage)

  • Computer “On Sensing” to prevent unknown states

  • User Optional Switch for Instant Off

  • Aux Output (Audio Amplifier Enable to avoid startup "clicks and pops)


The uSDC or Micro-Shut-Down-Controller is an electronically controlled automotive power switching device. It is primarily designed for the purpose of starting up or shutting down a personal computer used in a motor vehicle. It interfaces with a computer motherboard’s power switch header that would normally connect to the push-button switch on the front of a personal computer case. The uSDC includes a high current relay that will cut off or apply all power to the power supply of the personal computer to prevent any substantial current draw when the computer is not in use. The uSDC also provides a timing mechanism that is user selectable allowing the computer to remain “on” for an amount of time after the ignition has been turned off. The uSDC allows the user to mount the personal computer in remote locations (such as a trunk) and provides hands off method automating the startup and shutdown sequence while constantly monitoring the environmental conditions.


 uSDC20D Quick User Guide
 uSDC20D Input Power Connection Options 
 uSDC20D Full Specification 
 uSDC20D Aux Output Connection Options

Connection Diagram:


Connection Diagram Explained:


1.      The Yellow VIN connection should be a heavy gauge connection (12 or 10) gauge wire directly to the battery. This is the line where most of the current will flow.

2.      The Red ACC (Accessory) line can be light gauge wire. It connects to the Accessory line. This is the same line that turns on a car stereo only when the ignition is clicked into the second position.

3.      Red VOUT line connects to the + side of a 12 volt computer power supply or DC-AC inverter connected to a computer power supply. It should be heavy (12 or 10) gauge wire.

4.      The purple MB Power SW is a 2 pin jumper cable that is connected from the controller to the motherboards power switch. Make sure the polarity is correct, if it is backwards it won’t damage anything but it turn on or off the computer.

5.      The computer Power Sense cable consists of a signal Diode that connects from the controller to a 4 pin molex computer Hard Drive or CD-Rom Power connector. This is how the controller detects the computer is on so that is doesn’t inadvertently turn on/off the computer when it is already on or off. It also allows Power Down Mode to be very short.

6.      The Optional User Switch is a momentary switch that is pressed to turn off the computer faster, see the operational timing diagram.

7.      The Thick Black wires are heavy gauge Ground wires. The black wire going to the controller should be at least 18 gauge or thicker. It doesn’t carry much current, but is used for voltage sensing.

Specification Table:

Quick Specifications

uSDC20D Notes
Dimensions 1.85"L X 1.5"W X 1"H The circuit board is 0.062" thick.
Mounting Holes 4 - 0.125" grounded holes Mounting holes are located at (0.13",0.13"),(0.137",0.13"),(0.13",0.172") (0.137",0.172")
Operating Voltage 7 - 24 V The voltage range at which the unit will operate, this does not mean that the unit will output 12 volts over this range. It is a switch/relay device and not a power conversion device.
Power Terminals 0.052"Thick, 0.250"Wide Lug Lugs use standard off the shelf mating connectors (J1-J4)
Jumper Block 2x7, 0.1"Spacing  (JP1) Used for connecting signals to the motherboard, configuring options, and external power button. (JP1)
Standby Current

50 uA typical 

The amount of current the unit draws when the car is off, and all timers have expired (sleep state) the smaller, the longer the car can sit without draining the battery.
Max Operating Current < 80 mA The maximum amount of current the shutdown controller itself will draw when on and functioning
Operating Temperature  -40C to 85C The temperature at which the micro controller will operate and provide protection for the devices connected to it. (see range below for allowable computer range)
Max Load Current 20 A The maximum amount of current the computer can draw through the switch of the shutdown controller
Temperature Protection Yes The unit will detect if the ambient is too hot or too cold to function without damage. Will prevent power-up and initiate shutdown if out of the operating range (0 degrees C to 50 degrees C)
Voltage Sense / Protection Yes Ability to see how much voltage is coming from the battery, or detect that the car is running to turn on. Prevent over discharge.
Low Voltage Adjust Yes An adjustable pot is provided to fine tune the low voltage at which the shutdown controller will attempt to turn off the down stream device.
Over Voltage Protection Yes If too much voltage is connected to the shutdown controller, the transient suppressor will dissipate the energy and cause the fuse to blow
Optional Auxiliary Output Yes Will drive an external relay or turn on a power supply when operating. Useful for remote power (I.E. in-dash display) Includes a delay to support no "clicks or pops" when used as an Audio Amp Enable.
Adjustable Delay Time Yes An adjustable pot is provided to select the turn off timer (0-30 minutes)
Fuse Protection Yes If the shutdown controller or a device connected to the shutdown controller draws too much current due to a fault condition (Load Dump or other), the fuse will blow protecting downstream devices
Reverse Voltage Protection Yes If the Shutdown controller has it's input polarity reversed, it will cause the fuse to blow before damaging the unit and devices connected to it.
Optional Power Button Yes Manual override for the automatic startup and shutdown of the computer
Computer "On" Sensing Yes Allows the detection of the computer being shutdown by software so that the timed shutdown pulse, doesn't inadvertently turn the computer back on when it was suppose to stay off.
Ignition/Accessory Line Yes The unit is controlled by the accessory line similar to the way the radio is controlled by the keys turning on the ignition
Status LED Yes An LED to indicate which mode of the timing sequence the unit is in. Also used for fault conditions

General Timing Diagram:

Timing Diagram Explanation:


No PWR Mode:

When you first connect power to Vin of the shutdown controller it will power up into sleep mode. No PWR mode means that the permanently connected Vin terminal isn’t connected to the battery yet.


Sleep Mode:

After long periods activity the controller will go into this mode drawing minimal battery power.


Running Mode:

When the Accessory line goes high and VOUT gets connected to VIN (and the Relay clicks). The LED comes on solid and a time (t1) later the power up pulse (MB Power SW) is sent to the motherboard. At this point the computer turns on and starts booting. The engine would be started some time during this interval and the devices connected must be able to survive engine cranking. To exit running mode the Accessory line must go low. The engine is typically turned off before the Accessory circuit gets disconnected, but both can turn off simultaneously.

(t1) is 2 seconds by default


Count Down Mode:

In this mode the computer is waiting for an amount of time (t2) specified by the adjustment at P1. The LED flashes once per second in this mode. Fully clockwise allows maximum delay time and fully counter clockwise is minimal delay. Any time during this count down, the user switch can be pressed forcing the timer to go to zero and starting the Power Down Mode. If the Accessory signal comes back on during this time, the controller will go back into the middle of Running Mode not sending any pulses to the motherboard.

(t2) is adjustable between 0 and 30 minutes.


Power Down Mode:

After the previous timer expires, the power down pulse is sent to the motherboard (MB Power SW) The controller then waits for a time (t3) for the computer to shutdown or detects that the computer has turned off by monitoring the (Computer On) signal. The LED flashes twice per second in this mode. If the Accessory signal comes back on during this time the controller will wait for the computer to shut down and start over at the beginning of Running Mode sending a pulse to the motherboard to start back up.

(t3) is 90 seconds



Jumper Block Description:

Jumper Options:

User Modes:

0: Default User Mode, explained in the timing diagram. Start up pulse is sent when ACC goes high.

1: Voltage Sense Start Mode. In this mode the controller will wait until the car battery voltage is above 13 volts indicating that the engine is running and the alternator is charging the battery or keeping it charged. This mode is useful if you have a power supply that requires more than 12 volts to operate or your worried about the "Engine Cranking Transients." When the car is turned off (ACC goes low), the controller behaves the same as the default mode.

2: Temperature Sensor Disable.

3: Enables Temp Sensor Disable and Voltage Sense Start Mode


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