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[on:]

Hello!

Quick background on me, I come from a software background and trying to loearn about electronics but very new to electronics.

Right, I have my Arduino Mega and I have just got a new component (MLX90620 / mlx90620esf-bab-000-tu spec: http://www.melexis.com/Asset/Datasheet-IR-thermometer-16X4-sensor-array-MLX90620-DownloadLink-6099.aspx)

I'm very confused reading the data sheet. I cant work out if it takes a Vdd is ok using the 3v3 from the arduino or if I need to use a LM317 voltage regulator to take the voltage down to 2v6 ?? It seems to be ambiguous to me.

Can anyone advise me please as I dont want to blow the component up as it costs a bit and had to ship it from the USA!

Thanks
Tim

[Reply #1 on:]

I would first look for a dedicated 2V6 regulator and second an LM317L. You will also need a level shifter I personally recommend the device mentioned in
NXP App note AN10441 (attached) as it is Bi Directional and will work to 2.5V easily... FORGET the IC level shifters most suffer from large size because of un needed I/O many are single direction and there are only a few ic's that will work. This recommended (Highly By ME) does work, I haven't used it at 2V6 (I have at 3V3) but the app note does state that it will. I would recommend BSS138 Mosfets for the device. You Must use the correct level shifter, a mistake here could be very bad for the device... BTW how expensive was it???

Doc

[Reply #2 on:]

Thanks.

Regarding the level shifter, I cant find a AN10441 (im in the UK). Would the "ADG3301BKSZ" work (http://uk.farnell.com/analog-devices/adg3301bksz/translator-sgl-ll-bidir-6sc-70/dp/2067851) ?

The component was about £50

This component seems like its going to be a real learning curve just to wire up! I basically have no idea what im doing lol. Hopefully I work it out

I cant find any dedicated 2V6 regulator so I'm guessing I need to use the variable one

Thanks for the advice.
Tim

[Reply #3 on:]

ok, im trying to work this out still.

I understand now that you were suggesting what is described here: http://arduino.cc/playground/Main/I2CBi-directionalLevelShifter with the two mosfets.. I think im starting to understand a little more.

So I would use two mosfets for the shifting and the variable regulator to get the voltage I need.

[Reply #4 on:]

Tim I attached AN10441 to my first post. it's an application note from NXP explaining a simple 3V3 to 5V Bi Directional level shifter.
The answer to your question is I think so, Yes I believe so but read the app note. I had occasion to read the data sheet on the BSS138 and it looks fine. My circuit used 2N7000's first because the were what I had and second I was going from a 3V3 bus to a 5V bus so my situation would work well. IT did work, I modeled it in multisim 11 before I used it out of curiosity and it worked well. The proof was that I got my BMP085 sensor to work and very accurately at that. 50 pounds? about $85.00 Us. Wow I wanted an accurate IR temperature measurement tool for another project... But I might need to find an alternate source that is a little less expensive, perhaps I can use an aural (Ear) type IR thermometer I have one I found, it works but I have to convert C to F in my head, I've gotten pretty good at it but I am more interested in it as a means of detecting small energy changes.. I think I'll take a moment and read the LM317L Data Sheet again. I'll post the resistor values when I'm through.

Doc

[Reply #5 on:]

Ok,

So I have mocked up (badly) a diagram for regulating the 5v voltage down to 2v61 (which I believe is what I want) And level shifting the 5v Arduino SCL and SDA pins down to 2v61



Please can someone clever confirm I have this right

Thanks

[Reply #6 on:]

Yes You have it exactly right, I calculated 237.6 ohms so your regulator should work fine. I would make one change and that is the pull-ups make the 2V6 side 2K2 (1 mA current drain instead of ~200uA) and on the 5V side 4K7 instead of 10K (1mA instead of 470uA) the extra current although minimal will enhance noise immunity.

Doc

[Reply #7 on:]

Thanks Doc your a star

I have so much still to learn but it makes it less daunting when there is a good community of people willing to help other out.

Electronics have so many elements which are alien to me (coming from a programmer background) such as current. Im only familiar in thinking in one dimention - on/off!

Thanks
Tim

[Reply #8 on:]

In case it helps anyone else, I had created a working/interactive circuit diagram of the above level shifter (I couldn't do the regulator in this software) using some online java software:


http://www.falstad.com/circuit/#%24+1+5.0E-6+10.20027730826997+50+5.0+43%0AR+592+96+640+96+0+0+40.0+5.0+0.0+0.0+0.5%0AR+96+96+48+96+0+0+40.0+2.6+0.0+0.0+0.5%0Aw+96+96+96+128+0%0Aw+368+192+368+128+0%0Aw+304+208+304+240+0%0Aw+304+240+464+240+0%0Aw+464+240+464+208+0%0Ar+464+208+464+96+0+4700.0%0Ar+224+176+224+128+0+2200.0%0Aw+224+128+368+128+0%0Aw+224+176+128+176+0%0Aw+224+176+304+176+0%0Aw+464+96+592+96+0%0AM+544+208+624+208+0+2.5%0AL+64+176+16+176+0+0+false+2.6+0.0%0AL+544+304+624+304+0+0+false+5.0+0.0%0AM+64+288+16+288+0+1.5%0Aw+304+320+304+352+0%0Aw+544+352+544+304+0%0Aw+368+304+368+192+0%0Ar+160+288+160+240+0+2200.0%0Aw+64+288+160+288+0%0Aw+160+288+304+288+0%0Aw+160+240+160+128+0%0Aw+96+128+160+128+0%0Aw+160+128+224+128+0%0Ar+432+352+432+304+0+4700.0%0Aw+304+352+432+352+0%0Aw+432+352+544+352+0%0Aw+432+304+432+96+0%0Aw+464+96+432+96+0%0Aw+128+176+64+176+0%0Aw+544+208+464+208+0%0Af+368+192+304+192+0+1.5%0Af+368+304+304+304+0+1.5%0Ax+8+165+84+171+0+24+Input+%3E%0Ax+545+291+621+297+0+24+%3C+Input%0Ao+13+64+0+35+0.3125+9.765625E-5+0+-1%0Ao+16+64+0+34+0.3125+9.765625E-5+1+-1%0A

[Reply #9 on:]

How's the progress with connecting the MLX90620 to arduino? I'm thinking of getting one too. BTW. where did you buy the sensor?

C Lee

[Reply #10 on:]

I got the MLX90620 working with the arduino, you can find the sketch and circuit diagramm here: http://arduino.cc/forum/index.php/topic,126244.msg949212.html#msg949212