Help with my espresso controller

Hi,

First post and first Arduino/uC project.

I've designed and etched my own Arduino clone based on the single sided schematic to control an espresso machine (Via solid state relay).

[u]First question is around grounding.[/u]

I run a 12v cellphone charger as a power supply into the 7805 regulator. It just as 2 prongs into the wall so no "real" earth. The negative of the power supply is the ground of the board. Does this mean I have a floating ground. Is this ok?

Next up I have a Nokia CA-42 as a USB to TTL module which connects to laptop so now the Arduino board has a ground from 2 places the power supply and the USB ground of the laptop.

Can this cause any strange ground issues? I've already killed one CA-42 module not sure how.

I have had it up and running including the 1602 LCD and uploading code but at times I feel the uC is getting warm! (not hot but warm). I've had erratic results from the LCD and uC?, garbage on the screen, crashing etc And what appears to be contrast fading away after a while.

I'm running the LCD backlight (20ma LED) direct (via 47 ohm resistor) off the uC (Arduino digital 9). This should be ok right? I wanted to do this so I could fade with the PWM.

Any help including general comments on my design would be much appreciated. I WILL start over with a new board design if I have to but really don't want to! It goes with out saying that I should have done more prototyping on the bread board before I jumped into PCB design!

Images/schematic below

Kind Regards, Rhys

Nice photos.

Does this mean I have a floating ground. Is this ok?

Yes and yes.

so now the Arduino board has a ground from 2 places the power supply and the USB ground of the laptop

but as you said above the PSU ground is floating so there is no issue.

I’m running the LCD backlight (20ma LED) direct (via 47 ohm resistor) off the uC (Arduino digital 9).

What is the volts drop off your LED, at 42R this resistor is too low to limit the current to a safe level from the pin for a single LED. maximum current output for a pin is 40mA and you are best keeping it below 30mA.

You need some decoupling on the 328 chip.

Thanks GrumpyMike, acording to the site (where I aksed in the comments) http://www.sureelectronics.net/goods.php?id=123 The LED is 4.2v@20ma. This is where I got the value for the resistor from.

I've done some reading on decoupling and understand the idea behind it but could you give me a couple more clues as to where I might need it in my schematic? Pretty please;) Also is it ok to use these wee smd caps for this?

Ok, so I put a 330Ohm resistor on the LED and then measured the current with the DMM which showed 5.7ma. Using http://www.ohmslawcalculator.com/led_resistor_calculator.php I calculated that the LED must have a voltage drop of 3.1 volts not 4.2 as stated by the seller. Using 3.1v as the drop I calculated that I needed a ~100Ohm resistor to limit the current to 20ma. So far so good. :slight_smile:

In my schematic I show Pin4(digital0,int0) with a jumper to pin23. (analog0) which is where I run my 4 buttons. I did this in case I needed to fire the interrupt for my program since I wasn’t sure how I was going to write the software I used a jumper.

The idea is to analogread inside the interrupt and determine which button was pushed then set a variable which will be handled by the loop.

Is it ok to “short” these 2 pins together? For now I’m leaving the jumper off!

Thanks again,
Rhys

Ok Im really a bit stuck now with my grunding. I've now installed my controller in the espresso machine. The machine is all made of metal and very well earthed as it should be. Now I (think) have a voltage difference between ground (which is really just negative) of the arduino and the real earth. And I think it causing noise and strangeness! E.g when I touch the LCD screen it gets lines down it. And now it has started getting scrambled! How can I bring both grounds together when the input of the dc switchmod psu only has active and netural no earth connection?