Onewire DS18B20

[mauroForlimpopoli]

I included in my project the module "Onewire" and I added to my moddable two until 4 sensors DS18B20..
I have two problem:

1. When the cable of the sensors is very long (over 10 m) the module stops to work. This is because the wave form change so it's necessary to modify file owb_rmt.c. I changed some value of slot duration like OW_DURATION_RESET , OW_DURATION_SLOT.. and now it works. It could be nice to have the possibility to modify them dynamically.
2. DS18B20 have a scratchpad with an Eeprom with 3 byte. The first two byte are used for threshold alarm and the last for the resolution.
   In the module it seems that when this scratchpad is called the first byte is set to "78" (??) and the command "sensor.resolution = 9" no effect on the resolution.

[phoddie]

@wilberforce, can you help with this?

[wilberforce]

sure!

1. https://www.maximintegrated.com/en/design/technical-documents/tutorials/1/148.html

OW_DURATION_RESET , OW_DURATION_SLOT.. and now it works. It could be nice to have the possibility to modify them dynamically.

You could set this up so that these values in the manifest the same way these are set up:

moddable/modules/drivers/onewire/esp/modonewire.c

Lines 36 to 38 in e9742b4

	#ifndef MODDEF_ONEWIRE_RMT_TX_CHANNEL
	#define MODDEF_ONEWIRE_RMT_TX_CHANNEL (RMT_CHANNEL_3)
	#endif

Then you can override in your manifest and use the #defined MODDEF_ONEWIRE_DURATION_RESET and MODDEF_ONEWIRE_DURATION_SLOT

2. sensor.resolution = 9" no effect on the resolution.

So when you read the resolution after setting it does not come back as 9?
I use resoultion 12 most of the time as its most accurate.

Does the example work for you with a short run?

moddable/examples/drivers/onewire/main.js

Lines 63 to 69 in e9742b4

	sensor.resolution = 9;
	res = sensor.resolution;
	trace("res - should be 9 :", res, '\n');
	sensor.resolution = 12;
	res = sensor.resolution;
	trace("res - should be 12 :", res, '\n');

[phoddie]

(@wilberforce, thanks for sharing your expertise here!)

[mauroForlimpopoli]

Thank wilberforce,

1. sorry for my inexperience, but I can inset "OW_DURATION_RESET" in my Manifest, but how can I change it dynamically in the main.js ?
2. The example about the change of the resolution doesn't work. I used DS18B20 bought "online" and some of them are "Fake", the sensors measure temperature, but the Eeprom memory is not present (Sure of that !) Unfortunately my sensor are incapsulate, so its about impossible to verify the originality of the sensors Only in some of them I read the Eeprom. What I want to say is that if you tested the module about the write on the scratchpad and you haven't the problem maybe it depends from the sensors.

[wilberforce]

1. You would need to update the driber to have the set and gets method duration_reset(480) and duration_slot(75).
   So you have changed the resistor value recently - does this still require the timings to be changed?

2. Are you using the alarm? The set could be set up to preseve the other scratch pad value - however you usually set the resolution at start up - then this would not effect the alarm.

[mauroForlimpopoli]

Dear wilberforce,

1. I changed the resistor to 2,2k and now it goes better, but if the cable is longer I think to reduce the resistor until 1.5k.
2. I'm not using alarm, but I'm using the 2 byte of Eeprom to store inside some information about the sensors
   It seems the the function "set scratchpad(bytes)" is used continuously
   I think that this function

 const bus = this.bus;
 bus.reset();
 bus.select(this.id);
 bus.write(0x4E); // Write scratchpad
 for (let i = 0, length = bytes.length; i < length; i++) {
    bus.write(bytes[i]);
 }
 bus.select(this.id);
bus.write(0x48); // Copy to scratch pad
bus.reset();

when the "bytes" is undefined send the" 0x4E" command // Write scratchpad
then no byte is wrote,
but the command bus.select(this.id); send the value "Match Rom [55H]"
this value is accepted like first byte to write in the scratchpad and so in my next read always I find the value of 55H like !° byte of EEprom

Thank you for your assistance

Regards

[wilberforce]

Sorry, I have not used this feature.

It might be easier to store the device config in javascript - using the hex code of the device as an index.

[mauroForlimpopoli]

I think that this simple modification can avoid to write over the previous value

    const bus = this.bus;
    bus.reset();
    bus.select(this.id);
	if (bytes.length > 0) {
		bus.write(0x4E); // Write scratchpad
		bus.write(bytes[0]);
		bus.write(bytes[1]);
		bus.write(bytes[2]);
		bus.select(this.id);
    	bus.write(0x48); // Copy to scratch pad
	}
    bus.reset();

Let me know if you are agree
regards

[wilberforce]

I'm sure how this is trying to prevent overwrite unless you where sending more than 4 bytes.

Perhaps:

bytes.length > 0 should be bytes.length == 3 to check there are 3 bytes to write.
Also just checking you are not doing this while a temperature request going on as they can take up to 750ms to complete.

[wilberforce]

I ran the example code with a couple of DS18b20 ... this is what I see:

C:\Users\rhys\Projects\moddable\modules\drivers\onewire\onewire.js (45) # Break: step!
284273f90400005a
,28a39f840200005b
Found first:284273f90400005a
Found 2nd:28a39f840200005b
Sensor present: true
NULL Sensor present: false
res Before:12
res - should be 9 :9
res - should be 12 :12
0 284273f90400005a: 27.875
1 28a39f840200005b: 27.75
Got temp!27.5625

So the resolution does appear to set using the examples.

[mauroForlimpopoli]

I suppose the issue is in my sensors. I will buy other ones and I will test it again
Thank you very much!