Soda Vending Machine using PIC32

[gugu_gaga88]

Hi, I am new in using this forum. Currently, I am doing a project in developing a vending machine using PIC32 micro controller. I have already attached my circuit design but I am opened to any suggestion. I need to know whether my connections and circuit is okay or not. I am also confused on the relays connection. Any suggestion? Please verify my circuit. Thank you

 

[klystron]

Please give us you requirements / user stories of what the system must do?

 

[keith1200rs]

A PIC32 seems way over the top for a job that can be done with a PIC16/18.

It is normal to label the pins of the microcontroller, not just 1,2,3... Also, power connections are helpful!

Keith

 

[btbass]

Don't you think using a 32-bit Micro for a vending machine is a little bit of over-kill?
I'm sure an 8-bit Micro could do the job just as well.
It's like putting a V-8 Motor in a Mini.

With so many pins available, I don't think you need to share the LCD lines and the input key lines?

 

[keith1200rs]

Also, you have a ULN device and only using one output - a transistor would do. What is the serial EEPROM for - the PIC has plenty of built in storage. I don't know how much EEPROM it has but it probably supports self write Flash. You have no decoupling capacitors. You have no ICSP programing port.

Keith

 

[gugu_gaga88]

Thank you. I will re-design my circuit. I am actually designing vending machine monitoring system. Basically, the soda vending machine will be monitored by a host (my computer) through USB and also wireless communication. This monitoring system controls the inventory and financial managements of the vending machine using a database. I am using PHP and MySQL.

 

[tazcast]

hi @gugu_gaga88! can i ask what mechanism you are using to dispense the items?

 

[poorchava]

For some highly comunicative circuit pic32 might be good, but you may also consider 16-bit micros (like pic24). They have more than enought processing power and they have versions with multiple uarts/spi's/i2c's/can/usb device/usb host/ethernet controllers etc.Moreover, pic32mx795f512 is i believe the largest hog in pic32mx family and probably costs 5-10x more than what would actually be sufficient

As for the circuit itself: you might need a voltage level translator because PIC32 operates at 3.3V and most 2x16 LCDs operate at 5V. Even if you're only writing to the LCD and don't have to care about voltage tolerance of microcontroller input circuitry you might have a proiblem with logic levels. I've had a display which intepreted input as 'high' state from 4V upwards. This means that whatever you intend to output from 3.3V micro will be understood by the LCD as all 0's. I'd also add some input/output protection like series resistors for all the outputs, zener/clamping diodes on inputs. You also need a proper decoupling circuitry (basic would be 100nF ceramic cap at every pair of power pins, something larger like 1uF or 10uF somwehere nearby the chip and a small inductor in series on the power supply line for transient suppression). You also need to remember that most of higher range MCU's operate internally at 2.5V or 1.8V which means that they have a voltage regulator inside. Such voltage regulators often need some large external capacitors (e.g. 10uF). Read the datasheet throughoutly before using a microcontroller.