DS1820 with jm_ds1820_demo.spin only responds "no device"

StefanL38

Hi,

I'm trying to use Jonny Macs DS1820-Democode on my Propeller-Professional-Demo-Board (PPDB)

The only respond I get on serial terminal is "no device"

I tried the schematic provided in the democode

I have 10 sensors in a TO-92 package. Frontview GND DQ Vdd

DQ to Prop-Pin prop-pin has a 5k7-pullup-resistor
Vdd connected to +5V


I also tried the variant Vdd connected to GND (parasitic power-supply mode)
I also tried the variant Vdd connected to +3.3V

Then I changed the sensor.

Always the same result: demo-code responds "no device"

Now I'm pretty stumped what else I could do.

The code that is printed onto the sensors is "DALLAS DS1820"

Does anybody know of any trap I stepped in or any trick to make it work?

StefanL38

OK I got it.

It was something you can't see from more than 1m distance off my PPDB.

Using a 5.7 Ohm-resistor as pullup is a pretty-low resistance.
This resulted in a voltagedrop of only 0.3V which is not enough to get the bitbanging going

Now with a 4k3 resistor the sensor responds as expected

best regards

Stefan

MJB

StefanL38 wrote: »

Hi,
The code that is printed onto the sensors is "DALLAS DS1820"

the DS18B20 has 12 bits of resolution instead of the only 9 bits the old DS1820 has.

JonnyMac

You have to be very careful with 1-Wire devices. Personally, I always use a 3.3K pull-up to ensure that I get clean signals the line.