How to monitor an actuator's feedback line from a microcontroller?

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Skyland

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the AG-020-B electric actuator is controlled from a microcontroller. Terminal 1 is connected to the DC PSU GND, Terminal 2 is connected to the +24VDC via a high side Power MOSFET(TPS22810) as shown below. This is for power saving.



Low side MOSFET (AUIPS1021) Q5A and Q5B are used to control the opening/closing of the valve via terminal 3 and 4. The microcontroller I/O lines Valve_Ctrl_1a and Valve_Ctrl_1b provide a 3.3V signal.



- Comments are welcome regarding the power and switching circuitry.

- Any suggestion on how to monitor the feedback lines on terminal 8 and 10 from a microcontroller. A lamp is not suitable as the system will be enclosed in a box.
 

Any reason why you don't connect the aux contacts between ground and two processor inputs with pull-up resistors?
 

FvM said:
Any reason why you don't connect the aux contacts between ground and two processor inputs with pull-up resistors?
Click to expand...

are you referring to Valve_Ctrl_1a and Valve_Ctrl_1b?
 

are you referring to Valve_Ctrl_1a and Valve_Ctrl_1b?
Click to expand...
Surely not, this are processor output pins. Aux contacts (terminal 7 - 10) need to be connected to separate input pins. You'll connect it like any other input switch, e.g. push buttons.
 

I was not sure what you meant by aux. it is not possible to connect terminal 7-10 directly to the to the MCU as they have different voltages (3.3 and 24v). In addition, current will be too high for the MCU input pins.
I have solved this issue by using an optocoupler.
 

Hi,

I was not sure what you meant by aux.
Click to expand...
Top picture of post#1 clearly names terminals 7..10 as "AUX Contacts"

it is not possible to connect terminal 7-10 directly to the to the MCU as they have different voltages (3.3 and 24v).
Click to expand...
A simple (2 resistor) voltage divider for the microcontroller input may reduce 24V to 3.3V.

n addition, current will be too high for the MCU input pins.
Click to expand...
The microcontroller input current is determined by the microcontroller (Read it´s datasheet). This usually is in the low microamperes. It has nothing to do with load current or rated contact current.

Klaus
 

KlausST said:
A simple (2 resistor) voltage divider for the microcontroller input may reduce 24V to 3.3V.
Click to expand...

In this case the MCU will be pulled up to 24V when terminal 8 is disconnected
 

Hi,

No.
If you want to build a voltage divider to get proper microcontroller_level --> then use microcontoller_GND as reference for the voltage divider.

Klaus
 

KlausST said:
Hi,

No.
If you want to build a voltage divider to get proper microcontroller_level --> then use microcontoller_GND as reference for the voltage divider.

Klaus
Click to expand...

Not sure I get it, mind drawing a diagram?
 

Hi,

a voltage divider is simple: Two resistors in series.
* the bottom is connected to microcontroller_GND
* the center is connected to microcontoller_input_port
* the top is connected to the 24 signal line
Klaus
 

I wasn't really asking what a voltage divider is but how are you monitoring terminal 8 with what you explained?
 

Hi,

What do yu mean?

How many options do you see?
*****
* the bottom is connected to microcontroller_GND
* the center is connected to microcontoller_input_port
* the top is connected to the 24 signal line --> terminal 8
*****

Klaus
 

KlausST said:
Hi,

What do yu mean?

How many options do you see?
*****
* the bottom is connected to microcontroller_GND
* the center is connected to microcontoller_input_port
* the top is connected to the 24 signal line --> terminal 8
*****

Klaus
Click to expand...

Terminal 8 is unconnected by default, it needs to be connected to the 24V line for it to switch internally. You are saying the top part of the potential divider is connected to 24V which means not terminal 8 and it does not make sense. Again, a diagram might make it clearer. I have already solved this with an optocoupler, I am just curious what your option is

 

Hi,

No, it´s not connected to the 24V_supply, it´s connected to the 24V_signal = terminal 8

Why do you say now terminal 8 is not connected, but the schematic of post#1 shows a connection?

Klaus
 

That's from the datasheet of the actuator, the lamp is an example. I haven't understood your idea. Thanks for your help anyways
 



Is this what you meant?
 

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Hi,

Don't post a schematic that does not show your situation. It just causes confusion.
*****
Let's focus on what you wrote: "Terminal 8 is unconnected by default, "

If terminal 8 isn't connected.... where is the problem? Just connect it to the microcontroller with a pullup to 3V3. That's it.
No 24V, no optocoupler...

Klaus
 


I assume I can also connect directly from the MCU output pins (high imepdance by default and logic 0 to switch) to terminal 3 and 4 instead of using the low side switches?
 

Hi,

Here the microcontroller needs to drive current.
How much current?
And how much voltage?

Klaus
 

KlausST said:
Hi,

Here the microcontroller needs to drive current.
How much current?
And how much voltage?

Klaus
Click to expand...

The current is around 30mA according to the manufacturer. The voltage is not mentioned in the datasheet so I am not sure that's why I went for a low side switch to be safe.
 

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