Hi,there is something I don't understand. I relativly new to electronics.
I want to build a Midi Controller with 8 motorfaders (and other stuff too but that is not important to my problem right now).
I have one 74HC4051 Multiplexer to read the fader values that is working perfectly fine. I can read all 8 analog values (from 0 to 1023). Now I want to bring four dual-channel H-bridges (L293D) into the circuit for controlling the 8 motors. On a breadboard I successfully tested out the H-bridges (without any problems). But as soon as I bring only one of the L293Ds into my "main circuit" the max values I receive from the multiplexer (for the fader values) shrink from 1023 to ~1012. I also could measure a voltage drop on the vcc pin of the 4051 from ~4.98V to ~4.86V. The circuit is all wired in parallel to the Arduinos 5V/GND, the ICs as well as the 8 faders. If I understand it correctly, with parallel wiring I shouldnt experience any voltage drops at all or am I wrong? Since I'm planning to add more (like alot more) potentionmeters and buttons and a Nextion touch display, I'm wondering if I will run into much bigger problems.
Btw.: The same thing happens when I bring in the Nextion display instead of the H-bridges.
In an other test circuit, where I used five 4051 multiplexers, I did not have any problems like this. They all gave me normal values (1023 max)
cepexs:
If I understand it correctly, with parallel wiring I shouldnt experience any voltage drops at all or am I wrong?
Wiring in parallel only guarantees that the voltage will be the same across each load. If the power supply is supply is asked to provide more than its rated capacity, the voltage will sag but it will still be the same across each load.
It would be instructive to take see how much current each external load is drawing.
You have to remember wires are (low value) resistors, and if current flows through them there is a voltage drop.
Star-wiring is recommended when powering sensors and high-current loads from the same supply, such
that high currents never flow in wires supplying voltage to the sensors.
You can use thicker wire to reduce its resistance, but often connections have some resistance too,
and in particular breadboard connections which are not designed for high currents.
It was just a coincidence that I noticed the voltage drop. What I dont understand ist why the values I read from the multiplexer change as soon as i bring in a "foreign" IC (the "L293D") into the circuit.
In the attachment you can find a schematic of my current circuit.
Note: I know that only 4 of the motors are connected, since I didn't move on building since I noticed the misbehaving values.
What I dont understand ist why the values I read from the multiplexer change as soon as i bring in a "foreign" IC (the "L293D") into the circuit.
MarkT just told you why.
The current from the motor is being drawn on the wrong side of the sensors in your parallel wiring. This current causes a voltage drop of the voltage being delivered to your pots and so the pots won’t read the maximum any more.
You have to think about your current flow when arranging what order to do the parallel wiring, basically the current to the motors must not be allowed to go through the same wires as the sensor voltage and ground.
I also note you have no decoupling capacitors. One ceramic capacitor of 0.1uF should be across the power and ground of each chip.
Hi,
Can you post a picture of your project, so we can see your component layout?
This is the spec of your slider.
RSA0N11M9-LIN10K
ALPS linear motor-driven fader for studio mixing desks
These ALPS motor studio faders are the absolute benchmark in digital studio technology and digital lighting control technology. Metal housing for front and PCB assembly.
Motor voltage: 4 - 10 V DC
Starting current: 800 mA
Resistance: 10 kOhm
Slide path: 100 mm
Nominal voltage: 500 VAC / 10 VDC
Rated power: 200 mW
Tolerance: 20%
Dimensions (L x W x H): 146.5 x 18 x 26 mm
Hole spacing: 120 mm
Sliding force: 0.3 - 1.3 N
Synchronous operation: 2 db (middle)
Slide cycles: min. 30,000
Slider knob not included in delivery!
You will note the 800mA starting current.
Have you measured the running current of the motor?
What is your 9V supply?
What does the 9V supply do when you operate the slider motor?
I would be putting a least 1000uF across the 9V supply on the PCB and as @Grumpy_Mike has suggested some 0.1uF bypass capacitors at each of the power pins of the four ICs.
