How to share signal from a sensor?

Thread Starter

kevintu1987

Joined May 8, 2009
8
I am doing a hybrid-car project for my school. On the vehicle, I installed many sensors (RPM, temperature, current, voltage). Originally those sensors would be read only by one microcontroller. Now I want to install a data logging device for recording data off the same set of sensors. The problem is if the microcontroller and data logging device read the same signal, there would be loading effect..(different input impedances form a voltage divider) I really don't want to buy an extra set of the same sensors just for my data logger.

Is there a way to solve this?
 

MikeML

Joined Oct 2, 2009
5,444
Buffer the sensor signal with an op-amp voltage follower. If the sensor output is modified by it being connected to your uC, I would consider that to be bad design practice. Why isn't the sensor signal already buffered before it goes into the uC?
 

Thread Starter

kevintu1987

Joined May 8, 2009
8
The signal is buffed. It can be read by the uC alone. The problem I have now is I would like another device to read the same signal too. And I am trying to find a way to do it without having loading effect or buy another set of sensor.
 

kubeek

Joined Sep 20, 2005
5,718
If it is buffered, you can use as many devices connected to the buffer as the buffer allows. What input impedance do the uC and datalogger have? What is the buffer made of?
 

RimfireJim

Joined Apr 7, 2008
22
Kevintu1987,
You have a reasonable concern, but perhaps an unfounded one. Think of your microcontroller and data logger as DVMs. Does it not seem reasonable to connect two DVMs in parallel across the output of your sensors? Or one DVM plus one microcontroller or data logger, which we do all the time to check a sensor when troubleshooting a setup? Surely the input impedances of your two devices are both high enough that they shouldn't load the sensors.
 

Thread Starter

kevintu1987

Joined May 8, 2009
8
If it is buffered, you can use as many devices connected to the buffer as the buffer allows. What input impedance do the uC and datalogger have? What is the buffer made of?
uC is 50kOhm; I am not sure about data logger's impedance.

I put voltage followers before the inputs.

Kevintu1987,
You have a reasonable concern, but perhaps an unfounded one. Think of your microcontroller and data logger as DVMs. Does it not seem reasonable to connect two DVMs in parallel across the output of your sensors? Or one DVM plus one microcontroller or data logger, which we do all the time to check a sensor when troubleshooting a setup? Surely the input impedances of your two devices are both high enough that they shouldn't load the sensors.
That makes sense! Thanks!

Just in case if my devices load the sensors, would a voltage follower solve the problem?
 
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