Speed Demon 

Measure and display speed or elapsed time of any moving object:  freefall, ball on ramp

Measure and display sensor values: temp, light, ...

Portable (battery operated), affordable, simple, unique

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Speed of ball on ramp using the internal sensors of the Speed Demon in Speed Mode.

Elapsed Time in Free Fall using proximity sensors attached to Speed Demon in Elapsed Time Mode.

The Speed Demon

Multi-Function Extension for Microbit

Instructions and videos at www.funkey.net


The Speed Demon is a multi-function extension for Microbit which has these capabilities:


  • Measure the speed of falling or moving objects, display in cm/sec

  • Measure the elapsed time between two points of a moving or falling object

  • Measure the value of any analog sensor

  • Provide two pairs of direct input/output for sensors controlling outputs like LEDs


The Speed Demon is a stand-alone battery-powered device that does NOT require a computer. (However you CAN power it from the USB port of a computer, or a USB power pack)  It is available in two versions which operate identically:  with and without the Microbit.  Users who have a Microbit that they want to use with Speed Demon will load the “.hex” file onto the Microbit, then plug the Speed Demon into the Microbit.  The LED side of the Microbit should be inserted on the battery side of the Speed Demon.  The sensors are on the component side of the Speed Demon.




Push the blue button to turn the on The Speed Demon  It starts up in Speed mode, and displays the word “speed” on the LED display.  Pointing its sensors (the pair of lenses at the “bottom” of the board) will trigger the speed calculation.  Holding the Speed Demon either sideways or horizontally will track movement of an object that can be detected up to about 2 inches from the sensors.  The object can pass the sensors in either right to left or left to right direction.  Detection of an object by either sensor is shown by lighting the upper left and upper right LEDs.  If detection by both sensors occurs, the display will show the speed in cm/sec, and the display will repeat a second time.  The Speed Demon remembers the last 10 readings, and you can review them by pressing the “B” button on the Microbit.  Remember that the speed calculated and displayed by Speed Demon in this mode is that of the moving object as it passes the midpoint between the sensors.  So to determine speed, align the midpoint with the location you want to test.





You can enter the “Analog” mode by pressing the A button on the Microbit AFTER any display of readings has finished. In analog mode, the Speed Demon will continuously display the value of an analog sensor plugged into the “P0” port.  This port is labeled P0, 3V, GND, that is “signal”, power and ground, so the sensor must be connected using the header wires to this port in exactly that sequence.  Be SURE to connect the sensor correctly or you may get a short circuit and the chips may get VERY hot. Sensors may be marked with various symbols:  3V on the Speed Demon’s P0 port is the power connection and corresponds to the power pin on a sensor, which may be marked as VCC, + or other marking.  GND is ground on the P0 port and corresponds to the ground pin on a sensor, which may be marked GND, - or G.  The P0 is the “signal” and may be marked on the sensor as S, O, OUT or similar.



For some measurements in free fall or ramp experiments it can be desirable to know the elapsed time between two points in the motion of an object.  You can set ELAPSED TIME mode by pushing the A button again, after all display is finished.  When you enter this mode, the Speed Demon will display “elapsed”.  In this mode, you use external sensors, most likely Infrared Proximity sensors, to trigger the start and stop of timing a moving object.  Again be VERY CAREFUL to connect the leads to the right locations to avoid a short circuit and very hot components.  In Elapsed Time mode the ports 19 and 20 can be used with external Infrared Proximity sensors as “start and stop” triggers.  This is good for getting the elapsed time between two locations as an object passes by.  Successful detection of a moving object will be signaled by a single LED on the display in the upper right and upper left corners, then the elapsed time will be displayed.  Times are shown in milliseconds. If it gets out of phase, press the B button to reset.



This mode is always active.  You can plug sensors into Port 19 and it will control an LED on Port 2.  Likewise, Port 20 controls Port 13.  Remember that a raw LED has only 2 connections.  The longer one is positive BUT in this case is connected to the Speed Demon port’s signal pin, labeled  P2 on the board.  The shorter lead of a raw LED would be connected to the GND connection.  For this type of output, ignore the label HV on the port.  It’s the power connection, but not used with this type of configuration since the signal pin (P2 or P13) is providing the power to the LED on command from the sensor connected to the Port 19 or Port 20 pins.


Plotting Data from the Microbit: PlotSense

We have a separate .hex file program that can be used with the Speed Demon as well, described more fully in another document.  In short, its purpose is to use the Microbit to plot sensor data directly to a computer via the USB port.   Although it’s handy to use the Speed Demon to host your sensors, you can actually use this program directly on the Microbit without Speed Demon, or with another “breakout board” that gives access to Microbit ports 0, 1 and 2.


To use this feature, you install our custom application called PlotSense on your Mac or PC.  You load the PlotSense .hex file onto the Microbit and connect it using the microUSB cable.  Plug any analog sensors into the Microbit ports and you’ll be able to display their values in realtime on a graph, save the data, export the data, change the sampling rate from 30 milliseconds to minutes or hours, and freeze the display to make measurements on the screen.