How to make control decisions based on analog signal?

Thread Starter

fektom

Joined Aug 20, 2012
18
Hello everybody,

I am interested in making electric control decisions based on analog signals.
Many times I see machines which don't use digital signals but they are able to control electric behaviour based on analog signals.

For example I have a washing machine in my household. It has a heating part and it contains a termistor. The termistors current goes into a temperature selector and this is connected to the printed circuit board.

I know that termistor gives variable currents for variable temperatures, but I have a few questions related to other parts:

- I don't know what is the name of the electric part which "process" this signal (which is in the temperature selector)
- How it does it, and
- What is the output of it. Is this a standard dichotome signal, based on its position? For example it gives voltage if the selector is set to 30 and water is colder than 15 degree Celsius, and it does not give voltage, if the temperature is higher than mentioned?
 

Ya’akov

Joined Jan 27, 2019
9,071
They usual methods are:

A comparator, which provides a digital indication when comparing the input signal against a known voltage. This is a threshold device, and is only go or no go.

An ADC (Analog to Digital Converter), which converts the input voltage to a binary value, this resolution of which is determined by the number of bits the ADC can provide.

Each of these can be connected to a microcontroller and used programmatically.
 

drc_567

Joined Dec 29, 2008
1,156
... as far as analog decisions, in a general sense, take a look at the attached pdf ... the link for analog circuits. Within that circuit file, there are one or two interesting analog circuits in particular, which allow the addition and subtraction of analog voltage inputs. For example, say a parking lot drive-by sensor registers a +1 step voltage signal for every entering vehicle and a -1 step voltage signal for each exiting vehicle. So if the summation voltage eventually accumulates and reaches a maximum allowed value, indicating a full capacity lot, then a comparator circuit would allow a lot closure light and gate closure to be activated.
http://www.ti.com/analog-circuit/circuit-cookbook.html
 

dendad

Joined Feb 20, 2016
4,452
It sounds like you could benifit from an Arduino kit that includes a good set of instructions.
Then you can build things on a breadboard to test your ideas.
On Ebay or Amazon, look for "Arduino Starter Kit".
Then you can combine analog with digital.
 

MisterBill2

Joined Jan 23, 2018
18,176
Actually Yaakov gave the best answer in post #2, but there is a lot more to it. A comparator does indeed give an off/on signal based on the comparison of two voltages, and the thermister, as a temperature dependent resistor, with a little bit of additional circuitry, does provide a voltage that changes with temperature. But somehow that voltage that is used for the comparison must be calculated and delivered to the comparator terminal. So while the method is rather obvious once you understand it, it is not as simple as it sounds. The single advantage of using an aduino computer board is that you do not have to understand any of that, just follow the recipe and something may work. The downside is that even if it works, how much do you really understand about it. That has been my critisism of the arduino approach.
 
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