I'm new to PIC and CNC.. I've designed a circuit which is based on PIC18F4550, it drives 6 stepper motor and has a 4x4 keypad, Uses SD-Card and an USB connection to PC..
Please check if everthing is fine with the Circuit..
Thanking in advance.....
I'm new to PIC and CNC.. I've designed a circuit which is based on PIC18F4550, it drives 6 stepper motor and has a 4x4 keypad, Uses SD-Card and an USB connection to PC..
Please check if everthing is fine with the Circuit..
Thanking in advance.....
Looks reasonable, whats the application? I guess its to repeat a picture seen by the camera on the braille pads to allow a blind person to 'see' something, although I question the end to end speed you'll achieve...
On the circuit.. I assume you plan to use the 'weak pullup' feature of the PIC B port for the keypad. If not you should add pullups or pull downs on the input pins. I personally prefer pulldowns so that an unpressed key returns '0' not '1', I just don't like negative logic, but if you want to keep the component count for production then use the internal pullups. I'd put some resistors (5 - 10k ish) in series with the output pins drving the keyboard to avoid shorting pins together if someone presses two keys at the same time.
The steppers always turn in the same direction? Are they (guess) driving some cam arrangement to puch pins up and down?
You'd probably want some more decoupling on the 5v rail, a 10uF in parallel with the 100nF. You're not powering this from the USB, is there a reason for that?
Thanks irving2008,
My application s to convert just the text in image to braille.. I'm doing OCR in PC.. Then the text is transmitted via the USB to the device.. it then drives the stepper motors which punches d pins up and down(as u guessed).. I'm not powering it from the USB Coz i need my device to even work without d USB at times.
Sir, do i need to use a 10uF in parallel even if it is self powerd..?Quote:
Originally Posted by irving2008
I'm just a Computer Science student.. I've very little knowledge about all these..
Quote:
Originally Posted by irving2008
Samuel, it'll certainly work without it. Its just good practice to parallel filtering against high frequency transients (100nF) with something to handle lower frequency, longer time period 'brown-outs', especially if you have transients on the ground line from the steppers. If you are battery powered, or have a very good regulated power supply close to the circuit board you may not need it.Quote:
Originally Posted by Samuel Onesimus
Sir, Do you think the Circuit all right ..? Can i go ahead in implementing it..? Or i've any further changes to make??
What do you plan to program/debug your code with? I notice you haven't put any in-circuit programming (ICSP) connections on the circuit. I would recommend you do so even on the final build in case you need to reprogram the PIC later.Quote:
Originally Posted by Samuel Onesimus
Do you plan to build it straight off or breadboard it to try out? For something this simple you could go straight to PCB or build it on stripboard although I like to breadboard things first time - see the picture for one of my recent breadboards.
The PIC internal pull ups are not to be relied upon under any circumstances, they're just too weak for most applications. I don't know why uChip bothered with these.
I don't see any direction control from PIC to the motor driver.
A bulk capacitor (10uF tantulum) either side of the regulator will help prevent the regulator from oscillating.
I would 'isolate' the PIC step outputs to the driver with an optocoupler. this will prtect the PIC from catastrophic failure feedback.
I'd also place freewheeling diodes across the motor coils to the 12V rail - don't rely on the driver chip diodes, also small inductors on the power rails to prevent noise feedback and brownouts.
The UCN5804B only has a 1.5A current rating - If you using small light stepper motors this might be OK, but Stepper motors usually have high surge current around 3-10 amps depending on motor size - you might cook the chip in the first few steps, or it will get very hot and unreliable.
On the PCB try seperate the motor/driver cct ground plain/power rails from the PIC power.
With regard to USB, you might be able to run the PIC side, but not the motor drive side as USB (the last time I looked) can only run a max of 500mA on a port.
I would also keep my computer isolated from any machine control systems.
Hope this helps
:)