Ds1620

Pierson

I bought a DS1620 several years ago, and put it on the shelf.

I brought it out today and looked at the documentation I had printed. I have a BOE rev c from a BOEBOT serial.

I followed the schematic on the diagram and wired it up with nothing else on the breadboard. An eb500 is in the appmod slot, but no software running. Eventually I want to run a variety of sensors off the BOE and transmit the various data to my PC, but first I want to get this program running.

I cut and pasted the code from page 16/17 of the documentation, and plugged it into the a new page within the latest Stamp editor. I put a BS2 directive and a 2.5 directive in.

The program compiled without a hitch,· naturally. It downloaded and a debug window pops up and displays temperatures in both C and F. Problem is, it says 0 C/32 F. It's not quite that cold in my house.

Also, I don't see any reference to it, but on the same piece of foam that the DS1620 was inserted into, there is a small probe looking thing, maybe a quarter of an inch long, 1/8 inch in diameter, with two wires coming out of it. Was this part of the DS1620 app, or did I just put something which I have no idea any longer what it is on the same piece of foam?

Thanks for any assistance.

Pierson

Tracy Allen

The probe looking thing is probably a capacitor. If so, you will install it next to the DS1620 and it goes between the power pins to smooth out electrical noise. Is it not shown in the documentation? It might have printing on it with a + sign nearest a wire that is a little longer than the other one. The + and long wire should be connected to Vdd (pin 8 of the DS1620, and the short wire to Vss (pin 4). If there is not a + nor one wire longer than the other, then the polarity doesn't matter.

That probably doesn't have anything to do with the incorrect result. Check your wiring, and check that the power supply is connected to the DS1620.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

Pierson

Hi,

A more accurate descripton of the little 'can' is 1/4 inch long, 1/16 inch diameter, metal jacket with no printing on it, and two leads about 3/16 inch long.

You're probably right about the wiring. I used an unpolarized cap from the BOE kit (104 means .1, correct?)

From the documentation, I see that the pin on the DS1620 labeled VDD uses the cap.

On the breadboard, on the same row on the right of center, I have the VDD pin, then one side of the cap, then a JUMPER.

The cap goes into an empty row, and then a jumper from that same row goes to a hole in the VSS connector.

The JUMPER from the VDD row goes to a hole in the VDD connector.

I hope I interpreted the schematic correctly. As my knowledge is limited, and things quickly empty from my memory, does it matter that the cap connected to ground is between the 5 volt supply and the VDD pin?

Pierson

I tried removing the jumper from the VDD connector and the temperature went down to -1 C/ 30 F.

Tracy Allen

The little can you described sounds like it might be a 32kHz crystal. Maybe you got a DS1302 real time clock at the same time? The chip you think is a DS1620 has that printed on the top, right?

What you describe for the DS1620 wiring could be correct, but it is hard to visualize from the words. But it is almost surely a problem of the wiring or some simple thing. I don't know how the eb500 might affect the result, but try taking it out. Reduce the problem to the bare minimum.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

Pierson

I think the thermometer is defective.

Thanks Tracy. Confirmed, the chip is the DS1620. I wonder why I bought the crystal?

I neglected to mention it, but I removed the eb500 first thing after my first post. No change.

To make it more clear: I started by putting the cap between the power and the chip, and then changed it so the power was between the chip and the cap.

I also temporarily replaced the 1k resistor going between pin 1 on the chip and pin 0 with a regular jumper just to see if that made a difference, which it didn't. Everything else leads me to believe that it is wired correctly, as this is a three wire connection. I think I would get an error message, wouldn't I, if if the data line, clock, or reset were not connected correctly?

And the fact that the data changes when removing power leads me to believe that there is a problem with the chip.

For kicks I tried modifying the program by commenting out the temperature conversions, but still the same output.

I have a fresh 9 volt battery hooked up, the led is green, the jumper is set to Vdd.

Post Edited (Pierson) : 12/2/2007 10:57:37 PM GMT

Tracy Allen

Shappens sometimes, that a chip is defective. But in my experience with troubleshooting, if the chip is new, I make a conscious effort to discount that possibility. It is usually something else, a loose jumper wire, off by one on the pins, bent pin on the chip, something. Of course it is always nice to have two new chips as a backup to test the "defective" hypothesis. With a chip of unknown provenance, all bets are off.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

Tracy Allen

Zero C, 32F or close to it? That could be several things. But the data line back to the Stamp is stuck at zero. You are right, the circuit is pretty rudimentary. I can't vouch for the code. Parallax is very careful with the documentation. Did you download the latest version? Or post what you have, here.

Do you have a voltmeter? Or even an LED in series with a 1k resistor? Use that to check the power for 5 volts from pin 4 to pin 8 of the DS1620. Also write a little program like this:

DIRA = $F
DO
  OUTA = OUTA+1
  PAUSE 500
LOOP

That assumes that the DS1620 is hooked up to p0, p1, p2, right? You should see the binary pattern with periods of 1, 2 and 4 second at the pins on the DS1620.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

Pierson

I think my brain is defective.

You got me where I needed to go, Tracy. I never hooked up a ground to pin 4.

Once I did that, it showed room temperature. Then I got it to change temperature by holding a can of compressed air upside down and giving it a short blast, and the temperature dropped dramatically. It has just about returned to room temp.

Thank you. Now I need to get the StampPlot Lite working. Then, add the code for the eb500, and then figure out if I can get it to transmit data without needing Microsoft's Visual Studio.

Thanks again, Tracy.

Pierson