Bad lot of DS18B20 sensors?

I bought five digital sensing boards from ebay, marked Keyes on the board and Dallas 18B20 on the chip.
When I run the hacktronics sketch to find an address, it returns that no address is found. I have the power pins hooked as indicated on the board (and a red LED comes on) and the signal to digital pin 3 as in the sketch (attached). Am I doing something wrong, or could all five of these be bad? Thanks. (742 Bytes)

The DS18B20 requires a 4.7k pullup resistor. No such resistor...... no device or address found. Did you wire the DS18B20s up each with a pullup resistor?

modernhistorian: sensing boards from ebay, ........... a red LED comes on

It appears that your sensor is mounted on its own board and a power LED is included thereon, in which event one would expect the 4.7k pull up is also included, and you don't need another one. You need to check that. Indeed, if you HAVE added a 4.7k pullup, it may be the cause of your problem. I also imagine the connections are clearly marked and, with the power LED on, it is pretty hard wire it the wrong way round. If you are using a cheapo breadboard, the problem may be there.

I bought five digital sensing boards from ebay, marked Keyes on the board and Dallas 18B20 on the chip.

I suppose you’re using one breakout board at the time, not all five boards connected to one bus.
Because if you do, the 4k7 pull up becomes a <1k pull up.

Hi, Please give us a photo of the module..

I sell thousands of Keyes parts and they are usually very reliable...

@ terryking228

Do you have a diagram of that board. It could be that the 4k7 resistor is NOT a pull up resistor, but a current limiting resistor for the LED (indicator LED/resistor connected to 5volt?). In that case you still need an external 4k7 pull up resistor. Leo..

Hi, Photo please..Or what color is the board? Keyes has made 2 different ones..

Please see this page and try the code example there that we know works...

I don't THINK this one has a pullup. Checking...

The 4K7 pull-up is in series with the LED on that module so the LED blinks when there is activity on the data line.

Connecting five modules in parallel will not work as mentioned, the pullups or diodes will need to be removed from all but the last module in the chain. Try the modules one at a time to test.

Relabled transistors versus the DS18B20 :

Hi, Knowing your supplier, personally in my case, is best. I have had over 10,000 water-resistant (stainless steel case) DS18B20 based temperature sensors made by the same factory in Shenzhen over the last 4 years with extremely high reliability. They have assured me they use genuine Dallas parts and sent me unencapsulated samples from some batches on request.

@modernhistorian, did you get one of these running?? What color is it?