PCB250- shield for ArduServer2,with...

1) Monitored LED
2) DS18B20 temerature sensor
3) Additional analog sensor, which I used to measure ambient light.

(Notes arising from making instance "19Jan12", to be installed at 7NC)

(Expland description, or do xref to other)

=======================
Component selection....

You may well want to set up small circuits on a breadboard to check the correct orientation of the parts which you will eventually put in the PCB, and to check the performance with the components you are using.

All resistors: 1/4 watt adequate.

Pei1: A self oscillating "buzzer"... apply 5v acorss it, it should make a sound without further ado. Must not draw too much current. I used a "Projects Unlimited AI-175".

LED1 / Q1: These between them make a "home made" opto-isolator. It is fun to be able to see the LED lit or not, but if you want to replace them with a "normal" optoisolator, you could. The phototransistor's frequency of best sensitivity may inform your choice of color for the LED. (My sensor... a SFH300-3 phototransistor... seemed most responsive to a red LED, but my tests were far from "scientific". Wrapping the LED and phototansitor in a "tube" of tin foil seemed to improve performance, but be careful you don't short the leads of either device.)

My sensor (Q1) was a Siemens (Osram) SFH300-3, discussed further at my page on light sensors, http://www.arunet.co.uk/tkboyd/ec/ec1senslight.htm

R3 is the current limiting resistor to go inseries with the LED. The LED is powered from one of the Arduino digital pins. Choose a value for R3 that is low enough that the LED is reasonably bright, high enough that the current from the Arduino is not too high.

R4 is a "magic" resistor which helps the Dallas 1-Wire circuit perform well. It "shouldn't" be necessary, I don't think... but I believe it is worth including. I've heard that 4k7 is a good value for it. I have also used a 10k resistor here.

Q2: This can be just about any resistance-varies-with-whatever-is-sensed device you choose to put here... or you can just omit it! You may want to alter the value of R2 if you change the sensor. I used a SFH300-3 phototransistor.

R1 / R2: These are the resistors for the voltage dividers handling Q1 and Q2. I used 10k for both. (For more on voltage dividers, see 


======================
Before etching PCB....

1) Beware... your piezo buzzer might have different needs from the one I used.
(Ver 0-0, instance of 19Jan12 had pads slightly too far apart for my piezo, AI-175)

2) Consider the LED / light sensor (Q1), or opto-coupler you intend to use. The spacing of the 4 pads may need revising.

3) Consider the reset arrangements for the Arduino which will carry your shield. You may want access to the button on the Arduino, or you may wish to add a reset button on the shield.

4) If you are using an Arduino with ethernet, be sure there's room for the RJ-45.

5) Consider carefully the Arduino and Ethernet shield you intend to use PCB250 with. For a Sparkfun Pro Ethernet, I THINK the only lines used by that are D10-13.  (Which PCB250 does not.) Some other Arduinos and shields may be using some other lines, for things like selecting an SD card, etc, etc. This is just the usual "mixing shields" quagmore.


=====================
Parts orientation....

"Top" of board refers to the edge with R4.
"Left side" is as viewed from component side. The DS18B20, U1, is on the left side

Pei1: This is a polazized device. The "+" pin should go in the top hole.

U1: (Dallas 18B20 digital temperature sensor) The artwork for the PCB does show the correct orientation for the device: The flat face should be pointing to the right. However, it would probably be wise to separate this component from the immediate neighborhood of the PCB, and more particularly the Arudino under it. In theory, the wires can be quite long... meters. I would start with short wires... 20cm... and once everything is working well like that, see what degree of extension my system will tolerate. Even if U1 is taken off board, R4 can stay on the board. (More on this, and U1 orientation at http://sheepdogguides.com/arduino/ar3ne1tt.htm, if you want it. I hope what is here is already sufficient?)

LED1: The "flat" on one side of a typical LED usually identifies the leg to be connnected to the more negative point. On PCB250, that is the left hand hole. (If you insert it the wrong way around, it will just not light up, and can subsequently be reversed with no one the wiser, as long as an adequate R3 was present in the circuit at all times.)

Q1/Q2: If you are using phototransistors, they do need to be inserted in the PCB the right way around, the collector to the left in both cases. For the SFH300-3, that is the short leg, the one by the flat on the casing. (The collector goes to the more positive pad.)