<img src="the hobby shed.jpg" alt="the hobby shed picture">
The Hobbyshed.co.uk
INSPIRATION & SOLUTION
Return to Project Menu

TTL (Transistor to Transistor Logic)

Print pdf
There will be times when you purchase a circuit that does not appear to work no matter what you do. This is more than likely a circuit with a TTL output. (Transistor to Transistor Logic)

A case being the Infrared Sensors shown below where the output is TTL

Here is a very simple circuit which will convert the output into a signal that you can use to power either some LED’s or a relay. This circuit will work fine on any voltage from 5v to 24v, in this case the Infrared sensor requires 5v so best power this from the same power source. The only item you will need to check is the relay. This should have a 5-6v Coil
PARTS LIST
R1   1K 1/4w Resistor
D1   Diode 1N4148
D2   Diode 1N4148
TR1  Transistor BC547 npn
RL1   In this case a Miniature 5v Relay with 2 C/O sets

If you want to put this onto a PCB then here is the Copper Layout and the Component Layout.
Additions to the Parts List
PARTS LIST
PCB   Printed Circuit Board Single Sided 50mm x 22.0mm
TB1   3 way Terminal Block
TB2   3 way Terminal Block

Most sensors available at the moment are similar to the one opposite
They appear to be good value for money, however they will not
trigger anything other than a logic circuit.  The circuit above will
convert the trigger signal into something that can switch on a
relay.

From the relay you can now switch virtually anything you want, from
a warning LED, to Buzzer, Point Motors, and so on.

The above circuit is so simple it could all be fitted on the pin side of the
Relay, so not needing to produce a Printed Circuit Board.






The following diagram shows how the Infrared circuit is wired to the above Interface circuit.
The Infrared Sensor could be any type of Logic output circuit. Here it is wired to a 5v DC supply and the trigger is wired to the centre terminal on the interface circuit.
The output from the Interface is wired to a Green (ON) and Red (OFF) LED’s.
As the supply is above the working voltage of the LED’s, a dropping resistor must be used to reduce the voltage to the LED’s.