Bx24 Fader Example

Using PWD to Fading on and off an led/motor
(note, you could technically use this same method to accelerate/decelerate a DC motor)

In the same way you can use a transistor to drive a higher power device from the BX, you can also use a transistor to fade a device (such as a light, or a motor) on and off.

To do this, you should first start by wiring your transistor and device to the bx as seen in the following schematic.

Test your transistor as is. For example, if you have your BX wired to a transistor that connects a 12Volt Light circuit, make sure that when you call putpin(wiretotransistor, 1) on the bx, your 12V light turns on!.

(If you are having trouble with this step- go back through our transistor/relay lab.)

Up to now, when we use a transistor, basically the BX is sending the transistor 5Volts. These 5Volts close the transistor 'switch' and allow current to flow through our higher power circuit. A transistor however, is more then just an 'on/off' switch. A transistor can be used in a way (similar to a water faucet), to switch only partially on. We control how much the transistor is 'switching' by how much voltage we send the transistor from our BX.

To regulate voltage flow on the bx, we can use a command called pulseout.

Below, is an example that fades a 6 volt light on and off. I have connected PIN 5 on my bx to the transistor.

In this code I have created a sub routine called fader.

fader (pin, start, finish, speed)

Fader takes 4 arguments.

1) pin # that is connected to your Transistor.
2) The start pulse for your device. A value of 1 is the minimum. 1, for example, would give you the most dim point of your light.
3) The finish pulse for your light (i.e.. The brightest point.. you can play around with this number- increase the number if your light does not get bright enough)
4) Speed (is the delay between pulses.. which translates to how fast the light will fade on... this MUST BE A DECIMAL number)

Public pulse as integer

Sub Main()
call flashme(3)

'before running this code I should check that my transistor works
'normally, but simply running a test such as :
'call putpin(pintotransistor, 1)
'if this works, and my transistor is switched (And my device..ie. lights/etc.)
'are on,then proceed.

'fade light on
call fader(5, 1, 1000, 0.001) '(pin#, startpulse, endpulse, delay)

delay(2.0)

'fade light off- I just switch the values for startpulse and endpulse
call fader(5, 1000, 1, 0.001)

delay(2.0)

LOOP

end sub

sub fader(byVal pin as byte, byVal start as integer, byVal finish as integer, byVal speed as Single)

'if our start is less then our finish, this is our loop to fade ON
          if start < finish then
                    for pulse = start to finish
                              Call PulseOut(pin, pulse, 1)
                              delay(speed)
                    next
                    call putpin(pin, 1) 'turn the pin on when done
          end if

'if our start is greater then our finish, this is our loop to fade OFF
           if start > finish then '
                    for pulse = start to finish step -1
                              Call PulseOut(pin, pulse, 1)
                              delay(speed)
                    next
                    call putpin(pin, 0) 'make sure the pin is off when done
          end if

end sub