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# ttl and hall sensor

#### h-1366

Dec 31, 2022
2
Hello everyone, I am doing a cnc table project. At the end of each axis, there is a Hall sensor that limits the movement of stepper motors. What is the reason for connecting these sensors to the TTL circuit? What is the application of ttl circuit?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,185
Which TTL circuit?
TTL is commonly used to desribe a technology (TTL = Transistor Transistor Logic) which can be used (or was used in the past) to build a huge variety of logic circuits. Or do you use TTL in another sense? If so, please supply more detail.

#### h-1366

Dec 31, 2022
2
Thanks for your reply, this is a cnc table that another student has already worked on. Now I'm going to install a camera on the z-axis. In previous documentations, I came across this picture and in the description it is written that the Hall sensor is connected to TTL. I have attached the photo.

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• 1111.PNG
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#### kellys_eye

Jun 25, 2010
5,695
The implication is that the Hall Sensor itself doesn't necessarily output a logic level signal suitable for the detection circuitry (operating at TTL voltages - look it up) and that some form of 'level change' is to be applied to make them compatible.

In any digital circuit you may have to 'convert' many external signal sources as inputs and given that logic circuitry only 'sees' one of two possible states, this necessarily means some form of conversion.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,185
Whatever the TTL logic circuit does: without a schematic diagram and description it is impossible to know what the circuit does. As stated: TTL is only a general term for a specific type of logic circuits. It is not a description of functions.
AS @kellys_eye stated, the sensor output may have to be conditioned to match further processing by TTL logic, although this is not what the picture implies. The logic functions implemented in TTL may for example be used to register the sensor output when the respective axis is moving towards the sensor, but ignore the sensor output when the axis is moving away from the sensor. There is an infinity of other possibilities. As stated above: you'll need a schematic diagram and a description of the logic.

#### Keonte45

Aug 29, 2022
82
Hall sensors are used in CNC table projects to detect the end of travel for the stepper motors. These sensors work by detecting a change in the magnetic field, and when the motor reaches the end of its journey, the sensor detects the presence of a magnet and sends a signal to the control circuit to stop the motor. The reason for connecting these sensors to a TTL (transistor-transistor logic) circuit is that TTL is a digital logic family that provides a standardized, low-voltage, low-power digital signaling level, which is compatible with the digital control systems used in CNC machines. The application of the TTL circuit is to provide a digital signal that the control system can read to determine the motor's position and stop the motor when it reaches the end of its travel.

#### danadak

Feb 19, 2021
409
Microswitches also used on CNC limit detection :

Usually chained together in series on mill, NC switches, and if anyone
breaks mill stops. Use as a logic signal to mill controller board.

Regards, Dana.

#### MikeFleet1

Feb 8, 2023
1
Has anyone every used hall sensor and a current control motor to build a torque screwdriver that would limit the screwdrivers end torque by using the current control motor? I am trying to replace clutch screwdrivers like the one below with a smarter screwdriver.

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