I want to make a PCB for an esp32-cam based project with 2 drv8825.
However, I do not want to use the driver boards, since I am going to the trouble of making a PCB, I can directly solder the chips ON the board and end up with a smaller nicer board at the end.
However, althrough I can easely find the schematics for these driver boards and replicate them on easy-eda, going to PCB manufacturing is hard as it requires a whole lot of knowledge that I do not have (foot prints and part number mostly).
Does anyone have a project that they could share that has these and that I could directly import in easyEDA?
Looking at the standard drv8825 boards, I can see that they are 3 sizes of components.
Small ones (0805 I guess?): these are 5 caps and 2 resistors.
Mid size ones (I have no idea what foot print): the 2 sensing resistor by the look of it. Why are they a larger size than the others?
And a large capacitor (what foot print again?): the 4.7uF cap I assume?
Do you know what footprint these components are using?
Also, they are a number of filtering capacitors (VMM to ground, 100µf, 4.7µf and 2*0.1µf).
Since I will have 2 DRV8825 on my board side by side. Do I need to duplicate these or is it ok to only have them once?
Thanks,
Cyrille
Note: I am not an electronic guy... just good enough to put myself in troubles! Thanks for helping me!
The principle is simple - if the filters belong to circuits that will be common to two boards - for example, power and ground - then they can be combined. And for circuits that are separate for each board - for example, output pins - the filters will have to be duplicated
I advise you to look in the diagram for the nominal value of the element and then select one on site of the nearest store of electronic components, where you are going to order all this.
You may be faced with the fact that some elements are not in the desired footprint, but are in another. Choose those that are in the store(and change PCB project, of course), so that later you do not delay the assembly of the board for weeks due to the absence of one element. It is not necessary to repeat exactly the footprint that is on the original board. The footprint can be varied, as long as the element parameters (for example, capacitance, voltage and type for a capacitor) are suitable for the circuit.
Another question. Could anyone suggest a 5V to 12V DC-DC booster chip that I can use?
I need to power 2 0.3A per phase steppers and of course my ESP32-CAM. The total should be less than 1.5A@5V (most likely under 1A, but let us be safe!)
Probably 1206. The sense resistors operate at higher current than general purpose resistors, so use larger package for better heat dissipation.
Probably also 1206 or similar.
The "bulk" caps can be combined, but 0.1uF should be per IC. Note that these modules leave off a larger bulk cap which may be recommended.
It is always a good idea to check the datasheet to see what components are recommended.
If I were you, I would consider putting modules on your board for now to keep it simple. However, you will probably need to know the general principles for the rest of the design anyway.
0.3A / phase @ 3.6V * 2 motors = 4.3W
Add 0.3A @ 5V for the CPU = 1.5W
total = 5.8... In theory Better have a little bit of margin.. so let us say 7-10W (USB typically gives at least 7.5W)
"Why 12v booster, if all of your devices are no more than 5v ?"
Because the DRV8825 require >=9V as input voltage even if the coils for the steppers are only 3.6V.
So, 5V in, some components use 5V (or even 3.3V), 5V needs to be boosted up to 9+V for the stepper drivers which will step it down to 3.6V for the stepper motors!
No, I have never designed a boost convertor
I know the principle of operation, and anyhow, I would be most likely using an IC that does the heavy lifting.
But I do know that component selection, placement and ground plate design are important in this domain. But that I don't know enough about it!
I was looking at using a MT3608. They are dirt cheap (around 0.08$ on jlcpcb).
But I just know enough to know that I am unlikely to get it "right" without any help.
It's a very ambitious project for someone who as you said "am not an electronic guy... just good enough to put myself in troubles! ".
Circuit design and PCB layout is not something you learn overnight or can do in one day.
I will often spend a week or two reading datasheets, selecting parts, and drawing schematics. Sometimes doing spice simulations to make sure it has a good chance of working. Then maybe another week or two doing the layout, often going through several revisions "on paper" before I get something I like.
Proper thermal design is often completely ignored by many and often leads to premature board failure. It not only applies to the ICs but to all active and passive components as well.
I would not have the time to review your design to make sure that it has a good chance of working with the first iteration.
Stepper drivers are current drivers, they don't step down to the motor voltage, because the motor is inductive, they convert to a current. Higher supply voltage on the driver allows faster motor rotation by overcoming back-EMF.
Stepper motors have a current, resistance and inductance rating - voltage is not really relevant as inductance and back-EMF usually dominate its behaviour.
BTW it is far easier to simply piggy-back an existing DRV8825 module onto your board - then you can easily replace it if it blows up too.
Better have a little bit of margin.. so let us say 7-10W (USB typically gives at least 7.5W)