I've been making an schematic for a new project that consists of interacting with a DC motor (24v 6A) and a heating element by using an SSR. These components are going to be controlled by readings from 2 thermocouples (MAX31855) and displaying reading on a LCD screen.
I took some pieces from other projects, so Im not quite sure of some parts. For instance the 2N3904 between the arduino and the SSR or the IRLB8721 to control the 24v 6A motor. Does this schematic looks alright? Is there something I might be missing or I should replace? I did check every component and they seem to be alright with the voltage and current being used.
Im using a SY8205 as a DC-DC step down module, going from 24v to 5v to power up things such as the arduino itself or the lcd screen. 3v3 is used to power the MAX31855 modules directly from the arduino
Thanks in advance
The two MAX31855 take only 3mA in all so no problem there
https://datasheets.maximintegrated.com/en/ds/MAX31855.pdf
Also the MOSFET looks OK although its usual to put say a 10k from gate to ground.
You havent given a type number or a link (hint!) to the SSR.
My concerns:
1: there should be a star point for the ground because high currents (and switched) are present.
2: there should be decoupling for the various power supplies.
thanks for your reply and recommendations. I did some changes to the schematic, although given the lack of room, I added a symbol to represent the star ground of every element. Not sure though if the motor outlet need a conection to star ground too. I also added the resistor for the MOSFET and details for the SSR (SSR-40DA).
UPDATED: +5V to 5V pin instead of VIN
After some reading, I understood the need for a capacitor between the IC GND and VIN, but I'm not sure if there's a need somewhere else, maybe on the DC motor outlet? The original part of the circuit from where I took that, used a 470uF capacitor.
It looks like you have +5V from the power supply connected to Vin. Shuldn't that be connected to the +5V pin? I think Vin is for unregulated 7-12V.
Are the 24V Ground an 5V Ground connected? It isn't clear from the diagram.
Why is a transistor used to switch the SSR?
Did you want speed control on the 24V motor? Pin 2 is not a PWM pin.
you're right, in this scenario, the Nano should be powered from the 5V.
The 24v ground is not directly connected to the 5v ground, should they? you mean for the outlet, right?
The transistor is being used as an amplifier. I took this part of the circuit from another project in which they used a 3v powered Teensy 3.6. I though I would need it with the Nano too, but not quite sure.
The 24v motor is for a fan, the main idea is to regulate voltage in order to achieve different RPM profiles. I took the diagram from here
Look at the diagram you just posted. Arduino Ground is connected to 12V Ground.
I dont see a 12V supply, John?
However I'd be surprised if the 0V of the 24V input is not common with the 0V of the 5V output.
The capacitor ("10uF") is too small to be much use. Maybe stick with the 470uF?
https://www.jotrin.com/product/parts/SY8205
That may not be an optimal choice - its designed for an output of up to 5A so maybe not suited to the very light load presented by the arduino and display.
you saying I should add the green line connecting the 0V of the SY8205 to the 0V of the 24V outlet?
There's also a common ground from the MOSFET pin 3 to the 0V of the 5V (star ground)
As for the SY8205, I already have it so it would be a nice use case. I saw the efficiency for lower loads and it seems to be really good on low currents
How about adding it to a new drawing, instead of just indicating it vaguely with an arrow? Then we can talk about whether it's right or wrong and be really confident.
Again, your unusual and vague symbolism makes it hard to determine, but to me it looks like the green wire would bypass the MOSFET and just run the motor continuously.
The whole point of a schematic is to show all the connections exactly.
Does the SY8205 have DC continuity from 24V- to 5V- ?
Also the way you drew the MOSFET is unnecessarily unconventional. Why not make it easy on everyone and use the standard symbol?
I made the schematic in Eagle
