HELP! Temperature sensor

[Babich]

We made the temperature sensor with DS1621 and we have problem reading
temperature. It always displays temperature of -60 C (-76 F). (both of
them). We used following shematic
http://www.electronics-lab.com/projects/pc/010/

Please help us!!!

Sorry on my bad english

 

[Michael]

Babich wrote:

We made the temperature sensor with DS1621 and we have problem reading
temperature. It always displays temperature of -60 C (-76 F). (both of
them). We used following shematic
http://www.electronics-lab.com/projects/pc/010/

Please help us!!!

Sorry on my bad english

First of all, I've never used that DalSemi device. I have used only the
DS1820, but I've used it extensively. I've never read a DalSemi via COM
port, only with uCs. Nevertheless, some of what I write here might be
"all wet".

Your project uses a Win PC and COM port to read the DalSemi device(s).
There might be timing problems injected by Win. I know that DalSemi
1-wire devices have strict timing requirements. Have you scoped the COM
port and compared traces to sensor timing specs.? (I admit I don't know
that the device you're using is 1-wire; maybe it uses Data and Clock
lines. It's been a while since I read up on DalSemi temp. sensors.)

The temp. you're getting is (as I recall) the max. negative temp. that
the device can report, which corresponds to a large negative number.
Perhaps your sensor(s) are not responding at all. THe PC might simply
be reading a line that is normally high and never gets pulled low. Or
a device could be responding OK but the PC reads one or more bits too
early/late (Win timing problem). Or, if you're using addressing, that
address could be corrupted due to PC's incorrect timing.

Or ... all of your sensors are defective. This isn't such a far-fetched
idea; I once got three inoperative DS1820 from a distributer and found -
with DalSemi's tech. support - that *all* devices were defective.

I would go bug the guy who wrote the VBASIC code and ask for his help.

 

[Amnon Pomerants]

Hi
SCL and SDA pins are usally used to drive the I2C protocol.
You have connected it to the COM port (RS232 protocol) of the PC.
Such connecton requires a SW above the RS232 protocol that will comply with
the I2C protocol in order to drive the SCL/ SDA pins properly.
a simple TERMinal PC program will not do the above.
Amnon


"Babich" <danijel@spansko.net> wrote in message
news:c72igf$4u8$1@brown.net4u.hr...

We made the temperature sensor with DS1621 and we have problem reading
temperature. It always displays temperature of -60 C (-76 F). (both of
them). We used following shematic
http://www.electronics-lab.com/projects/pc/010/

Please help us!!!

Sorry on my bad english

 

[Anthony Fremont]

"Babich" <danijel@spansko.net> wrote in message
news:c72igf$4u8$1@brown.net4u.hr...

We made the temperature sensor with DS1621 and we have problem reading
temperature. It always displays temperature of -60 C (-76 F). (both of
them). We used following shematic
http://www.electronics-lab.com/projects/pc/010/

1) Try it on another computer, preferably not a laptop.

2) Make sure you have +5V on pin 8 of each IC.

3) Make sure diodes are inserted in correct direction.

4) Check for good clock signal on pin 2 when temp measurements occur.
You should see a nice square wave bursts (0-5V at approx 100khz)

5) You should see (what would appear to be) varying width pulses on pin
1 when the clock is occurring on pin 2 during measurements. This is
your temperature data.

Your device uses the Phillips IIC protocol (AKA two-wire) to
communicate, not Dallas 1-wire as another suggested. Also be sure that
you are actually using a 1621 (obsolete) and not the replacement 1631,
there are some differences that may affect you.

 

[Michael]

I took a close look at the schematic of your beastie. Forget my
comments about 1-wire in previous reply; your sensor isn't 1-wire.

Nevertheless, if you're trying to address a sensor on a multi-drop bus,
make sure you're sending the correct address.

Can you read a sensor address OK?