Author Topic: Wiring Actuator and Weight Sensor to a microcontroller  (Read 606 times)

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Offline Aequitas737Topic starter

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Wiring Actuator and Weight Sensor to a microcontroller
« on: October 20, 2013, 10:18:08 PM »
Hi guys I'm working on a project currently and have been having some trouble figuring out the wiring for my parts.

datasheet for weight sensor: http://www.farnell.com/datasheets/1430771.pdf
datasheet for linear actuator: http://www.farnell.com/datasheets/1443991.pdf

My first question is does this actuator have a way of knowing how much it has turned? other actuators I have seen have 5 wires, one which goes to the microcontroller which says the angle, but this one doesn't seem to have that?

And with the weight sensor I do not have any clue how to wire it up. What is a bridge configuration? Do the white and green wires go straight to the microcontroller ports? how do I go about powering the sensor?

Please any help anyone could provide would be greatly appreciated.
Thank you for your time,

Aequitas

Offline waltr

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Re: Wiring Actuator and Weight Sensor to a microcontroller
« Reply #1 on: October 21, 2013, 10:35:30 AM »
Re-read the data sheet for the weight sensor again. There is a schematic of what is inside the sensor.
Now, Google  "Whetstone Bridge" and read some more. There are many web sources explaining this and circuits to use.

The actuator uses a "Bi-Polar Stepper Motor". Google this learn how to drive this type of motor which will require a "Dual H-bridge" (Google this also). Typically one does need need position feedback since this motor turns a fixed amount per pulse (Resolution spec in data sheet). Just keep track of the number of pulses and some simple math to convert number of pulses to amount of linear motion.
A set of limit switches are typical to find the "Home" or start position and as saftey to prevent running into the end stops.
If there can be problems with stalling a linear position sensor is desired but on of these will cost.

Offline Aequitas737Topic starter

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Re: Wiring Actuator and Weight Sensor to a microcontroller
« Reply #2 on: October 21, 2013, 08:25:54 PM »
So for the weight sensor I put 10 volts across the green and black and then measure the voltage difference across the white and red by plugging it into the microcontroller ports?

Offline waltr

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Re: Wiring Actuator and Weight Sensor to a microcontroller
« Reply #3 on: October 22, 2013, 11:02:29 AM »
So for the weight sensor I put 10 volts across the green and black and then measure the voltage difference across the white and red by plugging it into the microcontroller ports?
Yes, but not directly to a micro-controller's analog (ADC) inputs.
First, I would be leery of getting 10V into the micro-controller pin which will destroy the micro-controller. So use 5V (assuming a 5V micro-controller) so this is always safe. Later you may use 10V excitation but ensure you have protection on the micro-controller pins.

Second, With the micro-controller's ground connect to the load cell's power ground (black wire) you can connect the two outputs (white/red wires) to two ADC inputs on the micro-controller. Read the ADC values then take the difference in software will give you the load cell differential output Voltage which is proportional to the load on the cell.

Third, the differential Voltage (white/red wires) is probably going to be fairly small (I could not find in the DS what the differential Voltage per kg is). The differential Voltage does increase with an increased load on the Cell. If the Full Scale (max weight on cell) differential Voltage output is small compared to the ADC reference Voltage then you will need to amplify the differential Voltage with some op-amps.
Once you add op-amps then its best to use a differential op-amp or instrument amp configuration to produce a single ended output Voltage. Then you only need one ADC input on the micro-controller.

The first step is connect a Voltmeter to the Cells outputs and apply power. Then measure the differential Voltage output while increasing the load on the Cell. This will tell you whay Voltage values you are dealing with and then you can go and design the circuits and/or ADC code.

Post back here your results from this testing for more help. BUT, do some more google searching on the terminology I just used (bolded text).

Offline Aequitas737Topic starter

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Re: Wiring Actuator and Weight Sensor to a microcontroller
« Reply #4 on: October 23, 2013, 08:39:21 PM »
quick testing shows it goes from 0.7v with no weight to 0mV is that enough to be able to read it directly? it doesn't seem like a lot
« Last Edit: October 24, 2013, 04:21:31 AM by Aequitas737 »

Offline jwatte

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Re: Wiring Actuator and Weight Sensor to a microcontroller
« Reply #5 on: October 23, 2013, 09:57:22 PM »
Quote
is that enough to be able to read it directly?

I don't know -- what does the data sheet for your microcontroller say?

Offline Aequitas737Topic starter

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Re: Wiring Actuator and Weight Sensor to a microcontroller
« Reply #6 on: October 24, 2013, 06:46:17 AM »
the chip is the HCS12, if i remember correctly it was like 65% of the voltage (5v) so 3.3. So i guess I need to use another opamp

Offline waltr

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Re: Wiring Actuator and Weight Sensor to a microcontroller
« Reply #7 on: October 24, 2013, 08:50:33 AM »
the chip is the HCS12, if i remember correctly it was like 65% of the voltage (5v) so 3.3. So i guess I need to use another opamp
Correct.
And better is to use an Instrument amp. (search for this as I suggested in above post).

 


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