Hardware design check please

Go To Last Post
9 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

So, I think I have completed the hardware design for my temperature controlled humidor but since it's my first electronics project since 1998 and my first ever uC project I would really like input on what I've missed, what I've done wrong and where I've made it harder than it should be ;']

The idea-- Humidor cooled via Peltier coolers. The controllers adc gets input from 4 sets of thermistors placed outside the box at ambient, on the hotside heatsinks of my TECs, on the coldside heatsinks of my TECs and inside the humidor and from a humidity sensor inside the humidor. After various calculations (P.I.D. and P.D. + condensation/soft start considerations) it sets PWM signals controlling the TECs, the hotside fans and the coldside fans. It also turns on circulation fans when the humidor is closed (detected by reed switches) and turns LEDs on and all internal fans and the TECs off when opened. It also outputs data on an LCD and sends data to a PC/Mac via USB for logging.
It's all powered from a 24V 4.5A regulated supply.

I _think_ that covers the description but will be happy to fill in anything I've missed.

Here are the schematics of the 3 sections; power, control, and usb/lcd. They seem to show up a bit small here, but if you right click and select "view image" they'll come up bigger.



Edward

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Just a limited observation. Did you meet the design criteria for the microprocessor external crystal circuit? There is also reset pin info.

AVR042: AVR Hardware Design Considerations:
http://www.atmel.com/dyn/resourc...

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Yup, followed that, though I haven't put an ESD protecting diode on Reset, anything special about an ESD protecting diodes beyond normal/zenner/schottky diodes?

Edward

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Zener and schottky diodes are no good for ESD protection - they need protection themselves! You need to use diodes suitable for ESD use - try transzorbs or specific ESD diodes. NXP have the BZA100

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Some non-AVR remarks:
FT232RL's status leds are reversed?
Backlight might need a series resistor?

Martin.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi,

You don't need to connect AREF to AVCC, you can just put a 0.1uF capacitor on AREF to GND. That way you can select the AREF using software, switching between internal reference(s) and AVCC. Also if you accidentally enable the internal ref, with the AREF pin wired to AVCC, you could damage the AVR.

-Colin

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Cool Mon! One needs a humidor in the tropical regions to keep one's herb moist!

Imagecraft compiler user

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

@MartMega: Oops, the FT232RL's status lines are active low but the LEDs are the wrong way round. Not according to the "datasheet" I have for the LCD (Chinese, ebay bought) but I will of course test with resistors first.
@c_oflynn: Thank you, I remember thinking that at the beginning then I forgot and connected it up ;']
@bobgardner: With ambient RH over 70% the weed is fine ;'] The cigars get too moist though. And with ambient temps that almost never go bellow 70F (21C) beetle larva hatch on the cigars. A friend of mine lost about $500US in cigars from an outbreak, hence the project ;']

Edward

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Update: Changed my LCD circuit to incorporate the 3wire system described here. Mainly since the LCD could be remote to the humidor and 14 conductor (or even 8 conductor for 4bit mode without R/W) cable is bulkier/more expensive/harder to find compared to 5 conductor.
The new schematic is:-

Edward