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prixsecco
Joined: 18 Dec 2011
Posts: 26
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| Melexis 90615 connection problem |
 Posted: Sun Dec 18, 2011 12:28 pm |
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Hello
I have problems with connection to my IR-Sensor.
Data Sheet see here: http://www.melexis.com/Assets/IR-sensor-thermometer-MLX90615-Datasheet-5477.aspx
I always get back a "0" (=DATA).
Used code is this:
| Code: |
#include <18F4550.h>
#fuses hs
#use delay(crystal = 20000000)
#use i2c(master, smbus, SCL=PIN_C7,SDA=PIN_C0) //slave,smbus, sda=C0 , scl=C5
#use rs232 (baud = 9600, xmit = pin_c6, rcv = pin_c4, bits=8)
void main(){
while(1)
{
i2c_start(); // Start condition
delay_ms(20);
i2c_write(0xB6); // Slave Address - write bit low - the '1' here is the bit number in the diagram, _not_ the value.... [0x5A<<1]
delay_ms(20);
i2c_write(0x07); // Register address
delay_ms(20);
I2C_start(); //Restart the bus
i2c_write(0xB7); // Slave Address - write bit high for a read (to change data direction)
DATA = i2c_read();
DATA1 = i2c_read();
DATA2 = i2c_read(0); //You need to _NACK_ the last byte
i2c_stop();
delay_ms(20);
printf("\n\rDATA: ");
printf("\n%4u",DATA);
}
}
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Hope anyone can help me... |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Dec 18, 2011 2:57 pm |
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Is the PIC running at +5v ? I would assume so, because you didn't say
you were using the "LF" version which can run at +3.3v.
The Melexis chip must not be run at +5v. The data sheet says +3.6v
is the maximum operating voltage. What voltage are you using for it ?
The i2c bus (or SMbus) must have pullup resistors on it. The pullups
should be connected to the same Vdd voltage as the Melexis chip uses.
Assuming your Melexis Vdd is +3.3v, you could use 3.3K resistors for the
pullups. (or 4.7K would be OK).
On page 6 of the MLX90615 data sheet, it says the output is typically valid
0.5 seconds after power-on reset. To be safe, you should have a delay
of lets say, 750 ms, at the beginning of main().
| Quote: | #use i2c(master, smbus, SCL=PIN_C7,SDA=PIN_C0) //slave,smbus, sda=C0 , scl=C5
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Your comment does not match the #use statement pins. Also, you are
not using the hardware pins, so the SMBUS parameter has no effect.
But you should not use the hardware i2c module, because it requires
Schmitt Trigger input levels, which are +4.0v for a PIC running at +5v.
Your pullups should not exceed +3.6v, so Schmitt Trigger inputs are not
appropriate for this design. Use TTL-level PIC input pins. Which means
you can't use Port C pins for this design. You have to use Port B for the
i2c bus. It's the only one that has TTL levels on its i/o pins.
(Note: Pins C4 and C5 are TTL, but they are input-only pins, and not i/o).
Your code that talks to the Melexis chip should be made into callable
functions. That's the best way to write a device driver. Currently you
are using inline code.
Also, I don't know your skill level, so I will add the following:
- SDA on the PIC must connect to SDA on the Melexis chip.
- SCL must go to SCL.
- There must be a ground connection between the PIC and the Melexis chip. |
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prixsecco
Joined: 18 Dec 2011
Posts: 26
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| Posted: Sun Dec 18, 2011 3:32 pm |
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Thanks for your fast and detailed answer.
I'm using 4.7k pullup-resistors. VDD Voltage is set to +3.3V.
Do i have to set VDD Voltage to +5.0 V? And do i need a voltage divider if using +5.0 V power supply because of the maximum voltage of 3.3V for the Melexis Sensor?
I tried several PIN connections, so you can ignore my comment you were talking...
Isn't SCL hardwired on PIN C7?
What i haven't understand is the connection at all. So i have to use Port B for the I2C connection? Some specific PINs of Port B?
I connected the Melexis Chip to the PIC as shown in figure 18 (page 21) at data sheet. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Dec 18, 2011 4:00 pm |
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| Quote: | VDD Voltage is set to +3.3V.
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Are you referring to the PIC or the Melexis chip ?
| Quote: | Do i have to set VDD Voltage to +5.0 V?
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According the the 18F4550 data sheet, in the Electrical Specifications
section, the "F" version of the PIC requires a minimum Vdd voltage of 4.2v.
It's possible that it will work at 3.3v for hobby testing purposes, but I
never do that, so I have no experience with it.
| Quote: | | Some specific PINs of Port B? |
Use any PortB pins except B6 and B7. Those pins are used for the ICD
programmer/debugger. You could use B0 for SDA and B1 for SCL.
For better help, post your CCS compiler version. |
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prixsecco
Joined: 18 Dec 2011
Posts: 26
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| Posted: Sun Dec 18, 2011 4:33 pm |
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According to the VDD voltage setting, i mean the PIC. (vdd voltage setting in MPLAB)
I'm using ccsc v. 4.3.0.285
Okay i will connect the sensor as you said on Port B and will change VDD to +5.0V. But do i need a voltage divider than? Or thus the 4.7k pullup resistors are protection enough for the sensor?
Last edited by prixsecco on Sun Dec 18, 2011 4:42 pm; edited 1 time in total |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Dec 18, 2011 4:38 pm |
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The 4.7K pullup resistors should be connected to +3.3v. That's high
enough to work with TTL-level inputs, such as pins B0 and B1. The PIC
can run at +5v. The pullups and the Melexis chip can run at +3.3v.
It will all work.
| Quote: | vdd voltage setting in MPLAB
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What does this mean ? Are you providing power to the board from the
ICD ? If so, do you have any method of providing +5v for the PIC, and
+3.3v for the pullups and the Melexis chip ? |
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prixsecco
Joined: 18 Dec 2011
Posts: 26
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| Posted: Sun Dec 18, 2011 4:47 pm |
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The board is powered by the PICKIT 2.
Simmiliar to this:
 |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Dec 18, 2011 5:19 pm |
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That means everything has to run at the same voltage. You don't have
a separate regulator on the board.
I tested the 18F4550 just now, while running it at 3.3v with a 20 MHz
crystal and it works, at least at room temperature. So use 3.3v on the
Pickit 2. Run both chips at 3.3v. |
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prixsecco
Joined: 18 Dec 2011
Posts: 26
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| Posted: Sun Dec 18, 2011 5:23 pm |
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Okay thanks for today. Your are great.
I will try it tomorrow and let you know than. |
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prixsecco
Joined: 18 Dec 2011
Posts: 26
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| Posted: Mon Dec 19, 2011 1:44 am |
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I changed the hardware connection and PIN definition in program code but now I get nothing out on Hyperterminal.
Whats the problem? |
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prixsecco
Joined: 18 Dec 2011
Posts: 26
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| Posted: Mon Jan 09, 2012 1:07 am |
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| Any idea?? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Jan 09, 2012 1:27 am |
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Yes, run this i2c bus scanner program and see if it finds the Melexis chip:
http://www.ccsinfo.com/forum/viewtopic.php?t=42368&start=4
You need to modify the program slightly to make it work with your
hardware. Change the #include for the PIC, and the #fuses, and the
#use delay(). Edit the #use i2c() statement so it uses your i2c pins.
Also edit the #use rs232() statement so it uses your pins. |
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prixsecco
Joined: 18 Dec 2011
Posts: 26
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| Posted: Mon Jan 09, 2012 1:54 am |
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Okey thank you. I tried it with the Melexis 90615 sensor. Nothing!
On Hyperterminal only "Start:" appears.
No True or False. ?!?
I tried it with another known working i2c sensor (not the Melexis 90615) and there I get a result.
(...1 chip found...)
Is the sensor dead? Or whats the problem? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Jan 09, 2012 12:48 pm |
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Are you certain that you have the Melexis chip connected correctly ?
The pin diagram shown on page 1 of the data sheet is a Top view.
But the diagram on page 5 is a Bottom view of the pins.
Are you sure that you wired it correctly ? Did you ever wire it
incorrectly, so that Vss and Vdd are reversed ? If so, you probably
destroyed the chip. |
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Mon Jan 09, 2012 1:22 pm |
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my 2 cents
with a compiler update
you may find the 18F45K20
to be of some help as well |
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