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Help on I2C


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#21 Frank Beerens

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Posted 07 April 2014 - 08:58 PM

1. Yes there  is.

2. The voltage is 4.23V is that high enough ?

3. Delay does not help.  When debugging i can make a delay also

4. the return value is zero, also when i disconnect the i2c bus ?

5. I tried it is returning zero but the brightness does nog change

 

any other things i can do ?



#22 mbrossett

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Posted 07 April 2014 - 09:15 PM

Since the "device.Execute(...)" is returning zero, that tells you the LCD is not acknowledging the I2C commands. Double check that the SCL and SDA lines aren't crossed. Also verify that the power to the LCD from the Netduino is greater than 4.7V. If it is not you will need to power the LCD from its own supply/regulator.



#23 Frank Beerens

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Posted 07 April 2014 - 09:20 PM

to be sure

i have a netduino plus 2 i connected sda/scl to the sd/sc connector

that is correct ?

 

i also have a netduino 2 there i connect to Analog 4 and 5?

that is correct ?



#24 mbrossett

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Posted 07 April 2014 - 09:24 PM

For the [latest versions of] Netduino 2 and 2 Plus you should connect the I2C lines to "SC" and "SD" as you are doing. What is the voltage to the LCD?



#25 Frank Beerens

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Posted 07 April 2014 - 09:25 PM

that is 5v? when i measure 4,23 Volt.

When measuring without any connection to the netduino the voltage is 4.68 volt.



#26 mbrossett

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Posted 07 April 2014 - 09:29 PM

So to make sure I understand you correctly, when you measure the 5V output of the Netduino without the LCD connected, the voltage is 4.68V...and with the LCD connected it is 4.23V?

 

If this is true, you must supply the LCD with its own 5V power supply. Do you have an old USB cell phone charge? If so, cut the connector off and wire it up to the LCD for 5V supply.



#27 Frank Beerens

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Posted 07 April 2014 - 09:31 PM

oke i will try tomorrow.

 

only the lcd part. The i2c part will be supplied from the netduino ?



#28 mbrossett

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Posted 07 April 2014 - 09:42 PM

Yes...you will have the power supply V+/V- wired up to VDD and VSS of the LCD, and the Netduino will need have SCL, SDA, and GND wired to the LCD.



#29 mbrossett

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Posted 07 April 2014 - 09:51 PM

I guess it just occurred to me that you are probably powering your Netduino from USB. That being said, if you have a power supply around (+7.5 to +9V DC, >500mA output) you could power your Netduino from that and may not need to wire up the LCD separate. If you have a power supply around that would be a quick test.



#30 Frank Beerens

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Posted 08 April 2014 - 05:51 AM

great i can just connect usb for debugging ?

 

and the external power supply where do i connect that just to the +5v and gnd of the netduino ?



#31 mbrossett

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Posted 08 April 2014 - 02:05 PM

If you use an external power supply for the Netduino (such as the one below) you will only need to use USB for debugging as you have stated. The power supply should be connected to the barrel input jack. Be sure to ensure that the power supply has a positive center barrel (this is most common type).

 

http://www.mouser.co...bXAYafurk4XukHd



#32 mbrossett

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Posted 08 April 2014 - 02:08 PM

Also if you do not have the right sized barrel on the power supply, you could wire it up to VIN and GND pins of the Netduino connector. Make sure the voltage of the supply is between 7.5VDC and 9VDC, though.



#33 Frank Beerens

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Posted 08 April 2014 - 05:46 PM

with the external power supply of 9VDC 500ma i get a voltage of 4,58VDC on the SDA line and also on the SCLLine.

 

but it does not get any tekst so i2c is still not working.

What could be the problem is the voltage still to low ? (many thanks for your help until now).



#34 mbrossett

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Posted 08 April 2014 - 11:54 PM

Yeah, the voltage may still be too low. You should power it up from its own supply. Also make sure you are checking the return value of the I2C execute commands...that will tell you if the LCD is acknowledging the commands.

#35 mbrossett

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Posted 11 April 2014 - 04:08 AM

Are you making any progress Frank?



#36 Frank Beerens

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Posted 11 April 2014 - 04:59 PM

not really

i sold a more powerfull powersupply (1500 mA).  I thought that would help.

The voltage on the SD line is 4,62 VDC now. But it does not seem to help.

If i have a seperate powersupply for the display is it only for the display itself or also for the i2c logic ?

i can look if have any which i can cut the wires.



#37 mbrossett

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Posted 11 April 2014 - 05:34 PM

Looking at the Netduino schematics I think it should more than capable of providing the LCD power without a large voltage drop...that being said let's figure out what is causing your 0.4V voltage drop and then we should be able to fix it. Please measure the following voltages...

1) VIN_PROTECTED (U1 pin 3 on Netduino)
2) +5.0V (U1 pin 4 on Netduino)
3) +5V_HEADER (at the connector on Netduino)
4) VDD (at the LCD input connector)
5) SDA/SCL (idle voltage)

Make these measurements with your 1500mA power supply connected to the Netduino and the LCD power, ground, SDA, and SCL pins connected to the Netduino connector.

#38 Frank Beerens

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Posted 11 April 2014 - 08:05 PM

1. 8.70 VDC

2. 4.67 VDC

3. 4.67 VDC

4. 4.65 VDC

5. 0 VDC

 

when i disconnect the SDA from the netduino i have 4,58 VDC with connection to the netduino it is 0VDC.

i'm getting crazy it was 4,58 VDC before when it was connected.



#39 Frank Beerens

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Posted 11 April 2014 - 09:05 PM

tried again and now it has a voltage also when connected

so

 

1. 8.68VDC

2. 4.67 VDC

3. 4.67 VDC (it is the same connector or what do you mean ?)

4. 4.67 VDC

5. 4.59 VDC



#40 mbrossett

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Posted 12 April 2014 - 04:35 AM

This is strange. Out of curiosity is the USB cable disconnected while taking these measurements?

So what we need to measure is the (1) input to the 5V regulator (should be about 8.7V), (2) the output of the 5V regulator (should be 5V when not powered by USB), (3) the voltage on the output side of the MOSFET load switch for the 5V header (should be around 4.95V), and (5) the voltage at the LCD (should be around 4.9V or more if you have proper cabling). When making these measurements your reference should be the power supply input negative terminal at the input barrel connector.

I'm surprised that the voltage output of the 5V regulator is so low.




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