Digital buffer or line driver help

[Urahara]

Hi

A sensor I am tinkering with states that a line buffer or driver is needed if the output pin is more than 12 inches from the microcontroller. My microcontroller will be abt 60 inches away from the sensor

Any recommendations for a simple buffer or driver? Where in the specs will it say it can drive up to 60 inches away?

Do I make sense at all?

Thks!

 

[AlainB]

If the sensor is outputting only highs and lows, I would beleive that a Schmitt trigger near the microcontroller would buffer and clean this output very well. I am not competent to recommend you one in particular but personally, as a buffer, I use the 74HC14 witch is an Hex inverting Schmitt trigger.

Alain

 

[ericgibbs]

Hi

A sensor I am tinkering with states that a line buffer or driver is needed if the output pin is more than 12 inches from the microcontroller. My microcontroller will be abt 60 inches away from the sensor

Any recommendations for a simple buffer or driver? Where in the specs will it say it can drive up to 60 inches away?

Do I make sense at all?

Thks!

hi,
Is your sensor outputting analog or digital data.?

What range of switching rates/frequencies are you expecting from the sensor.
Please post a datasheet for the sensor.

 

[Urahara]

hi,
Is your sensor outputting analog or digital data.?

What range of switching rates/frequencies are you expecting from the sensor.
Please post a datasheet for the sensor.

Hi AlainB, Eric

Thks for the prompt response!

The sensor is a photodiode, the TSL230R, which converts lights into frequency and outputs a square wave up to 100kHz. I am using the CCP pin of the microcontroller to capture and count the rising edges in a sec. Attached is the datasheet.View attachment tsl230r-lf-e3..pdf

I am wondering if the buffer or driver can be placed at the sensor end rather than the microcontroller.

 

[ericgibbs]

Hi AlainB, Eric

Thks for the prompt response!

The sensor is a photodiode, the TSL230R, which converts lights into frequency and outputs a square wave up to 100kHz. I am using the CCP pin of the microcontroller to capture and count the rising edges in a sec. Attached is the datasheet.View attachment 41256

I am wondering if the buffer or driver can be placed at the sensor end rather than the microcontroller.

hi,
In that case I would do as Alain suggests a 74HC14 inverter at the PD end of the wire.

 

[Urahara]

Just for my own knowledge, what specs of the 74HC14 would say how far the signal can be driven?

 

[ericgibbs]

Just for my own knowledge, what specs of the 74HC14 would say how far the signal can be driven?

hi,
The datasheet states a +/-15mA source sink at the specified output levels.

 

[crutschow]

Just for my own knowledge, what specs of the 74HC14 would say how far the signal can be driven?

How far a signal can be driven depends upon the characteristics of the line being driven and the frequency of the signal. It's not a simple answer.

For low frequency signals, your main concern is driving the capacitance of the line, which is proportional to the line length and the type of line. Coax has a capacitance that varies from about 15pF to 30pF per foot, while twisted pair varies from about 12 to 20pF per ft.

If you need to have high frequency signals travel a significant distance (typically >1/4 of the frequency period at the cable propagation speed), then you may need to use controlled impedance transmission lines such as coax or shielded twisted pair. These will need a driver that can drive the characteristic impedance of the line, which typically varies from 50 to 93Ω for coax, and about 100Ω to 150Ω for twisted pair. Coax require single-ended drivers and receivers (single output and input) and twisted pair require differential drivers and receivers.

 

[Roff]

Re Crutschow's comments, I concur, except the critical parameter is transition (rise & fall) times, not data rate per se. If the risetime is greater than 3 times the delay of the transmission line, the line "looks" like capacitance. If the line is longer (or the risetime faster), then reflections will occur if the line is not properly terminated.
https://www.electro-tech-online.com/custompdfs/2010/04/CriticalLength.pdf