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1  Using Arduino / General Electronics / Re: Strange effect of a level shifter between Atmega (3.3v) <=> SIM900 (2.8v) on: March 14, 2013, 10:55:47 am
Good ! I understand what you said about the power increase. By the way it show that the port A is an output.

It seems that you are not taling about the same chip.

The one I use have reversed OE pin. ( /OE )



I have all /OE and DIR to GND, so it good for B to A for the two bus I think.

But I still cant understand why the serial link 1A2 1B2 works like a charm, and on the other hand, the simple power on on 2A2 2B2 only works when the SIM900 is already on and is going to shutdown.

Maybe it is just about the 2.8VVD_EXT from the SIM900 module that is not realy good when the SIM900 is off. But I still see 2.9 V on it.
2  Using Arduino / General Electronics / Re: Strange effect of a level shifter between Atmega (3.3v) <=> SIM900 (2.8v) on: March 11, 2013, 12:55:42 pm
I have made a mistake, it was TP1 not TP2 in this : When I put TP2 to GND with a wire, the power current increase to 0.1 A (idle 0.05 A), why ?

So I corrected my post.

Yes tp2 connects to the output of a ''245, If it is high you are potentially damaging the '245 by shorting tp2 to ground. If you NEED to pull PT2 down add a series resistor between the gate and TP2 470R should be within device limits

Bob
I think that TP2 is wired on the INPUT side of the level sifter, so It should be OK.
3  Using Arduino / General Electronics / Strange effect of a level shifter between Atmega (3.3v) <=> SIM900 (2.8v) on: March 11, 2013, 05:58:21 am
Hello,

I'am using a level shifter IC to convert 3.3v TX to 2.8RX of a SIM900 (GSM module) It works great.
But, I also want to use it on the PWR_PIN that switch on the SIM900. (because It have unused pins)

The SIM900 Datasheet said :


I have wired the level sifter like this :

TP1 is on the GSM. TP2 is on the ATMEGA.

The level sifter is http://www.ti.com/product/sn74avc4t245?qgpn=sn74avc4t245

Why if I pull TP2 to low, then TP1 dont goes low.
But, if I take a wire and set TP1 to GND, the SIM900 switch on, and then if I pull TP2 to low from the ATMEGA it shutdown properly the SIM900 (so the level shifter works like it should). Can you help me to undersand why ?

When I put TP1 to GND with a wire, the power current increase to 0.1 A (idle 0.05 A), why ?


Big thanks to you

J
4  Using Arduino / Motors, Mechanics, and Power / Re: adjustable voltage regulator arithmetic/calculations (NCP1117) on: January 30, 2013, 01:02:59 pm
Ok, I understand, It's because IADJ is not related to CADJ !

But, how to know IADJ ?
5  Using Arduino / Motors, Mechanics, and Power / adjustable voltage regulator arithmetic/calculations (NCP1117) on: January 30, 2013, 09:12:17 am
Hello,

I'am trying to "configure" an adjustable voltage regulator to make 4.3V, but I should be stupid, I can't understand how in the datasheet.


For me the problem is about Cadj, I dont understand how to deal with it.

The datasheet :
http://www.onsemi.com/pub_link/Collateral/NCP1117-D.PDF

Thanks for your help,

Julien N
6  Using Arduino / Sensors / ADS1234 : 24bits load cell adc on: November 27, 2012, 03:06:28 pm
Hello,

I'am playing with an ADS1234 (it's a 24 bits adc made for load cell) and a load cell. I have already get this working with an ADS1231 chip. (same as ADS1234 but with only one input, the ADS1234 have 4).

The datasheet of the ADS1234 : http://www.ti.com/lit/ds/symlink/ads1232.pdf
The datasheet of the ADS1231 : http://www.ti.com/lit/ds/symlink/ads1231.pdf

With the ADS1234 the RDY pin don't goes low. So I can't read data.
One time yesterday it worked during 5 minutes. But I cant understand why.

Maybe the capacitor ?

I used one like this, of 100nF = 0.1µF

The chip is wired like this :
1 => VDD
2 => GND
3 => GND
4 => NC
5 => GND
6 => GND
7 => GND
8 => GND
9 => CAPACITOR
10 => CAPACITOR
11 => LOAD CELL OUT +
12 => LOAD CELL OUT -
13 => NC
14 => NC
15 => NC
16 => NC
17 => NC
18 => NC
19 => GND
20 => VCC
21 => GND
22 => VCC
23 => GND
24 => GND
25 => GND
26 => VCC
27 => NC or UC SPI SCLK
28 => NC or UC SPI MISO

What I am doing wrong ?
I need to take a global view.

What can I test ?

I have already tried with an another chip, but it don't change anything.

I must be something very stupid ....

Thanks for your help !
7  Using Arduino / Networking, Protocols, and Devices / Re: SPI Load cell chip ADS1231 on: November 07, 2012, 03:09:16 am
I don't think that is a SPI mode 0 device. It appears to be a mode 1 device. It has a clock that is LOW with HIGH pulses (CPOL = 0) and propagates on the rising edge (CPHA = 1).
http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus

Ohoho you are right !
8  Using Arduino / Networking, Protocols, and Devices / SPI Load cell chip ADS1231 on: November 06, 2012, 05:17:59 pm
Hi


I'am playing with an ADS1231 (http://www.ti.com/lit/ds/sbas414c/sbas414c.pdf) chip to read a load cell value.



Code:
#include <SPI.h>

const int dataReadyPin = 9;
void setup() {
  Serial.begin(9600);
  SPI.begin();
  SPI.setDataMode(SPI_MODE0);
  pinMode(dataReadyPin, INPUT);
}

void loop() {
  if (digitalRead(dataReadyPin) == LOW) {
    unsigned int result1 = 0;
    byte inByte = 0;
    for (int c = 0; c <= 3; c++) {
      result = result << 8;
      inByte = SPI.transfer(0x00);
      Serial.print(inByte);
      Serial.print("<<");
      result = result | inByte;
    }
    Serial.print("=");
    Serial.println(result);
    delay(1000);
  }
}

With a progressive pressure on the load cell (with my hand) the output looks like :
Code:
1+139+170+255+=43775
1+200+219+127+=56191
2+156+31+255+=8191
3+59+255+255+=65535
3+225+95+255+=24575
0+175+159+127+=40831 <== Problem !
4+7+15+255+=4095

I thinks it's realy noisy, but it seems to be working.


So my questions about this :
- My line with "if (digitalRead(dataReadyPin) == LOW)" is really bad, because it will not be only true in falling. I don't want to use an interrupt, so how can I do that ?
- Is there a cleaner way to read the SPI bus than writing 0 on it ?
- About noise, have you any clues ?
- What do you think about the "problem" of 0 on the output ?

Thank you very mutch.

Jul
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