# New Some Urgent Help With Wiring.

Hi guys,

I've got a circuit that I need to wire, which uses an Arduino, breadboard, LCD, and pressure sensor. The Sensor is measuring absolute pressure and displaying it in PSI on the LCD. The program is loaded onto the Arduino, and I need to test it. I had someone help me from outside my country with the circuitry, and they've sent me a schematic that I'm struggling to follow.

My knowledge of circuitry is limited, and I urgently need help as this is a circuit I require for Wednesday next.

Here is the schematic I was sent -> http://i62.tinypic.com/1g4xav.jpg

(I have two 47k resistors.)

Here is a picture of the equipment I have -> http://i57.tinypic.com/rm0iua.png

I would appreciate if someone could simplify right down for me.

Thank you guys!

What value is shown in your diagram that you posted ?

I would appreciate if someone could simplify right down for me.

It doesn’t get any simpler.

The first link you posted is a drawing showing exactly how the equipment should be connected - I don't understand how it could be made any clearer.

raschemmel: Either you don't know the Resistor color code or you did not research I2C interfaces or both. Why are you telling us you have two 47k resistors ? What does that have to do with anything ? What value is shown in your diagram that you posted ? Start with that.

I would appreciate if someone could simplify right down for me.

It doesn't get any simpler. What is your question ?

The two resistors in the schematic are 47k.

I'm unsure how the resistors are connected in the diagram.

Find a schematic or pinout diagram of an arduino.
Pins A4 & A5 are SDA & SCL pins for I2C. If you do know what I2C is then you should know that these pins require 4.7k to 10k ohm Pullup resistors to +5V.

Asylum15: The two resistors in the schematic are 47k.

I'm unsure how the resistors are connected in the diagram.

The resistors in the diagram are coloured Yellow, Violet, Orange on my PC which is 47k in my reference document. I have no idea whether that value is appropriate or not.

It would help if you describe how you think the resistors should be connected because then, if you are wrong, we can explain. I suspect you won't be wrong.

...R

47k is a very weak pull up for I2C.
4k7 would be more reasonable.

Thank you Robin. I had open it with a photo viewer to see the color. I stand corrected. Anyway, as I said, and Robin agrees,

these pins require 4.7k to 10k ohm Pullup resistors to +5V

The correct pullup resistance for the I2C bus depends on the total capacitance on the bus and the frequency you want to operate the bus at.

The formula from the ATmega168 datasheet (which I believe comes from the official I2C spec) is –

Freq<100kHz===>Rmin=[Vcc?0.4V)/3mA],Rmax=1000ns/Cbus
Freq>100kHz===>Rmin=[Vcc?0.4V)/3mA],Rmax=300ns/Cbus

The Microchip 24LC256 specifies a maximum pin capacitance of 10pF (which is fairly typical). Count up the number of devices you have in parallel on the bus and use the formula above to calculate a range of values that will work.

For a bus freq > 100khz, with a bus Capacitance of 60pF, the Max Resistor value is 5k ohm.