Voltage with level shifter ~1.2V


50 posts   Page 2 of 2   1, 2
by techpaul » Sun Nov 04, 2012 7:22 pm
Do you have a Rev 1 or Rev2 Pi?
Does you board have mounting holes on it?

Your Fritzing diagram of the level translater seems to bear no resemblenec on pinout to the pictures on the Adafruit site.

If you disconnect the GPIO connector and try i2cdetect -y 1 does the system still crash?
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by chrney » Sun Nov 04, 2012 8:06 pm
Rev 1, no mounting holes, black audio-connector (the rev2 seem to have a light blue one).

The level shifter is not alike, that's true - I simply could not find this in a Fritzing library. I hope you get the point anyway.

It still crashes, when I try with i2cdetect -y 1.
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by chrney » Sun Nov 04, 2012 8:17 pm
Found the level shifter, replaced here:

http://i.imgur.com/eKe1M.png

LCD's I²C from left to right: GND, VCC, SCL, SDA.
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by techpaul » Sun Nov 04, 2012 8:30 pm
According to your latest Fitzving diagram, you connected

TXD to Breadboard 0V. The circuit has no GND (0V) according to your diagram.

You connected Breadboard 0V to A1 and B1 I have no way of being sure that you have a connection between

Connect Breadboard 0V with separate wires as follows to

GPIO GND pin 6 NOT pin 8
Level Shifter GND pin (two wires)
LCD 0V/GND
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by techpaul » Sun Nov 04, 2012 8:33 pm
Your diagram suggests you are connected to wrong pins on the display which are on the back board coming out the side of the display, not on the maion row which are different signals.
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by chrney » Sun Nov 04, 2012 8:43 pm
It is connected to pin 6, not 8, thats a mistake in the diagram.

I connected the four wires to the I2c-backboard, GND, VCC, and the two that started with S. Nothing to the 16 pins on the LCD itself.
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by techpaul » Sun Nov 04, 2012 9:25 pm
chrney wrote:It is connected to pin 6, not 8, thats a mistake in the diagram.

I connected the four wires to the I2c-backboard, GND, VCC, and the two that started with S. Nothing to the 16 pins on the LCD itself.

I suggest you check with multimeter on resistance setting, that the wires atually make connection from the connector actual pins to the actual pins of the desitinations. Update your wiring and or diagram to match exactly, as it is difficlut to help with mistakes on diagrams.

Connect GND to the actual GND pins on the Level Shifter

When powered up check actual voltages again as I do not believe you are actually wired up as you claim to be and have a missing connection or swapped connections.
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by chrney » Mon Nov 05, 2012 4:39 pm
http://i.imgur.com/u9psY.jpg
= updated drawing. Sorry for the confusion in the prior drawing.

http://www.lottastaxi.com/movie.MOV
= movie with actual wiring. I hope you can see anything. It was the best way of illustrating this. It's just like I have the wiring on the drawing above. It's 4.3 meg, the movie.

Still nothing, but when checking i2cdetect with parameter 1, it does not hang anymore. But I can still not find the device.
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by techpaul » Mon Nov 05, 2012 4:54 pm
chrney wrote:http://i.imgur.com/u9psY.jpg
= updated drawing. Sorry for the confusion in the prior drawing.

http://www.lottastaxi.com/movie.MOV
= movie with actual wiring. I hope you can see anything. It was the best way of illustrating this. It's just like I have the wiring on the drawing above. It's 4.3 meg, the movie.

Still nothing, but when checking i2cdetect with parameter 1, it does not hang anymore. But I can still not find the device.

I am not familiar with the breakout cable you are using, but it looks to me that 5V and 0V (2 and 6 respecively) make sense as to the pins they are connected to on the cable. The white wire does NOT look like it is connected to pin 1 or 17 actually looks more like pin 10. SDA and SCl are on adjacent pins but your cables are connected to it looks like 1 nd 5

With power off on Pi check which pins wires are connected to on the GPIO connector using a multimeter.
I would put the 0V and 5V wires to the LCD on the Breadboard bus bars to be sure of connections.

Obviously doing some changes from rechecking has stopped the crash problem due to miswiring.
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by chrney » Mon Nov 05, 2012 6:21 pm
Hi Paul,

at first, I'd like you to know that I really am very thankful for all the help!

The white wire was connected to pin 1, the SCL and SDA are connected to pin 5 and 3. I made a new video, where I removed all the unnecessary wiring on the Pi itself. Check it here:

http://www.youtube.com/watch?v=JxwaZZKTHjw

Would you mind to check this once again?

How do you mean, how do I check the things with the multimeter? I checked the VCC, SDA and SCL against GND on the display, they all show about 4.5V, likewise on the breadboard HL-side. Breadboard LV side it's 3.3V.
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by techpaul » Mon Nov 05, 2012 7:15 pm
chrney wrote:Hi Paul,
......
How do you mean, how do I check the things with the multimeter? I checked the VCC, SDA and SCL against GND on the display, they all show about 4.5V, likewise on the breadboard HL-side. Breadboard LV side it's 3.3V.

On resistance setting power off Pi, and check to pins on GPIO connector to your circuit to be sure you are connected correctly.
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by chrney » Mon Nov 05, 2012 7:20 pm
Sorry, I still don't get it - as I said, I am quite a noob here. So:

a) should I power off the Pi? That is, to pull the power cord? Not likely, but anyway, checking.
b) Where should I place the plus-"stick" of the multimeter,
c) where the minus-"stick"?
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by techpaul » Mon Nov 05, 2012 7:24 pm
chrney wrote:Hi Paul,

at first, I'd like you to know that I really am very thankful for all the help!

The white wire was connected to pin 1, the SCL and SDA are connected to pin 5 and 3. I made a new video, where I removed all the unnecessary wiring on the Pi itself. Check it here:

http://www.youtube.com/watch?v=JxwaZZKTHjw

Would you mind to check this once again?

Well appears connected correctly.

What value are the resistors?

If still does not work, try

Removing resistors (this is a must do for THIS test)
Connect LCD SDA and SCL to GPIO SDA and SCL

Then try i2cdetect on both controllers again.
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by chrney » Mon Nov 05, 2012 7:29 pm
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by techpaul » Mon Nov 05, 2012 7:30 pm
chrney wrote:Sorry, I still don't get it - as I said, I am quite a noob here. So:

a) should I power off the Pi? That is, to pull the power cord? Not likely, but anyway, checking.
b) Where should I place the plus-"stick" of the multimeter,
c) where the minus-"stick"?

Yes pull power off Pi you cannot do resistance tests with power in a circuit.
Set meter to resistnace range 200 or 2k ohm range
Plus and minus does not matter at this point, as the meter tests the resistance between the leads
  • One lead on one end of a connection at the GPIO connector (preferably the back of the connector)
  • Other lead on the pin point of the level converter
Resistance should be less than 1 ohm for a good connection
Similarly check leads to the LCD from GPIO (5V and gnd) and leads from level shifter to LCD
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by techpaul » Mon Nov 05, 2012 7:32 pm
chrney wrote:http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=150915954990

= Resistors.

They look OK when used after level shifter.

Dont know what country you are in but these sorts of things can be got from many places, ebay for resistors should be last resort. Especially when shipping from abroad.

Do a google or whatever search for electronic components in your country. Lots of people will have them
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by chrney » Mon Nov 05, 2012 7:34 pm
Without resistors = no change

SDA och SCL connected to GPIOs = display flickering, meassured 3.3v on the display's SDA and SCL - but, it finds the device on i2cdetect -y 0.
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by techpaul » Mon Nov 05, 2012 7:37 pm
chrney wrote:Without resistors = no change

SDA och SCL connected to GPIOs = display flickering, meassured 3.3v on the display's SDA and SCL - but, it finds the device on i2cdetect -y 0.

Suggests level converter either broken or bad connection. Flicker suggests other problem could be a loose connection or not being initialised.. Could also be a faulty display.

I would try in that configuration to get the software initialisation and simple text up just a couple of characters to see iof it works.
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by chrney » Mon Nov 05, 2012 7:39 pm
I tested the display the GPIO-way (connecting 12 out of 16 wires) - that worked just fine. So the display is good then, I guess?
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by techpaul » Mon Nov 05, 2012 7:40 pm
chrney wrote:I tested the display the GPIO-way (connecting 12 out of 16 wires) - that worked just fine. So the display is good then, I guess?

Probably can you write text to it ?
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by chrney » Mon Nov 05, 2012 7:42 pm
Yes, yes i can.
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by techpaul » Mon Nov 05, 2012 7:46 pm
chrney wrote:Yes, yes i can.

Looks like working then my money is on level shifter or wiring problems, every additional connection or connection point is potential for problems, always keep number of connections to a minimum
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by chrney » Mon Nov 05, 2012 7:50 pm
How come that I always just get 4.5V? Should that not be 5V, straight through?
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by techpaul » Mon Nov 05, 2012 8:17 pm
chrney wrote:How come that I always just get 4.5V? Should that not be 5V, straight through?

You probaly have 4.7V on Pi and loss on the cables making it 4.5V.

Alternatively you have a a poor PSU only giving 4.5V, or a thin USB cable or the PSU dropping volts due to too large a loadfor the PSU, or a combination of all of the above.
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by techpaul » Mon Nov 05, 2012 8:18 pm
techpaul wrote:
chrney wrote:How come that I always just get 4.5V? Should that not be 5V, straight through?

You probaly have 4.7V on Pi and loss on the cables making it 4.5V.

Alternatively you have a a poor PSU only giving 4.5V, or a thin USB cable or the PSU dropping volts due to too large a loadfor the PSU, or a combination of all of the above.

Alternatively You meter is not accurate or has poor lead connection.
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