3-wires components (DS1620, DS1302, etc.) max distance?

jmspaggi

Hi,

At what maximal distance canwe put a 3-wire component and still have it working fine? I'm mainly talking for DS1620 sensor.

Any idea?

Thanks,

JM

Mike Green

The DS1620 and similar SPI-based sensors use logic levels and are not designed for use at any significant distance. With careful attention to impedance and noise, you might be able to get them to work reliably at a distance of tens of feet. You'd need to slow down the clock and allow more time for signal propagation.

1-wire temperature sensors would be better. They're designed for signal runs of hundreds of feet and Philips has application notes on how to use them over long signal runs.

It's not very useful to ask about "maximal distances" because it all depends on what you use for the signal drivers, clock frequency, signal voltages, cabling and what the noise environment might be.

jmspaggi

Hi Mike,

Thanks for your prompt reply. My project is to pu a DS1620 on my roof, which is about 25 feets away from my Javelin. So based on what you said, this might works. If it does not work, then I will try to slow down the "push", and if it's still not working, I will try with a 1-wire. Do you have any 1-wire reference that I might use?

Regards,

JM

ElectricAye

Could you use a DS18B20 digital thermometer? It's a one-wire device. There's an object for it in the Object Exchange for the Propeller that allows you to chain about 8 of them on one line, but it might be buried in an Object entitled Spin One Wire or something like that. If you're interested and can't find it, let me know and I'll dig up the exact location. As I recall, that particular version needs a small modification to give you negative numbers.

Hope that helps,
Mark

jmspaggi

Ho, seems to be very useful and exactly what I need. I will try to find how to buy those parts.

I found some posts on the forum regarding the DS18B20 so I will start with that. My challenge will be to convert that for the Javelin [noparse];)[/noparse]

Thanks!

JM

ElectricAye

JM,
you can get DS18B20's at Digikey.com Note that there is a "parasitic" version (has a PAR in the number) and a normal version (for example, DS18B20+-ND). I know that the normal version is compatible with the object for the Spin One Wire. But it's possible that the parasitic version is NOT interchangeable with the normal version.

Hope that helps,

Mark

jmspaggi

Hi Mark,

I found 4 different references. DS18B20Z+-ND, SS18B20+-ND, DS18B20U+-ND and DS18B20+PAR-ND.18B20 +-ND, U+-ND and Z+-ND are "simply" different format of the same component.

For the PAR version, it means "Derives power from data line (“parasite power&#8221[noparse];)[/noparse]—does not need a local power supply", which I think can be very usefull, but will the "data" line be able to power 8 components? Not sure. Anyway, it's not a big deal to add 1 wire so I think I will go with the "non parasite" version.

Also, do you know if there is any sensor able to go up to 180°C (356°F)?

Thanks,

JM

ElectricAye

jmspaggi said...


Also, do you know if there is any sensor able to go up to 180°C (356°F)?

Hi JM,

You might let people here know what you want to do with this thermal sensor. There are people on this forum that are a lot smarter than me who could answer that question off the top of their head. Note that 180 C is right about the temperature of melting some solders, so keep that in mind when designing your system. I'm sure there are thermocouples that could easily read those temperatures but I'm not experienced with those.

Maybe take a look at Parallax's thermocouple kit:
www.parallax.com/StoreSearchResults/tabid/768/txtSearch/thermocouple/List/0/SortField/4/ProductID/96/Default.aspx


Also, if you don't need to be very accurate, you could use a non-contact approach to measuring the temperature, a sensor that can read the infrared coming off of whatever it is. For example, Parallax sells this

www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/520/Default.aspx?txtSearch=thermal+sensor

They also sell a version with a smaller field of view (FOV) so the sensor won't be gazing all around.

Rather than titling your post by a specific component number, you might consider re-posting with a more generic question: "How can I measure temperatures around 180 C?" or something like that. Give that a try and I'm sure the gurus here will come to your rescue.

hope that helps,
Mark



Post Edited (ElectricAye) : 4/27/2009 6:31:25 PM GMT

jmspaggi

Just did it [noparse];)[/noparse]

In fact, I need 3 high-temp sensors, and some low-temp. So I will start to "play" with the DS18B20 until I find a solution for the high-temp.

Thanks again for your help.

JM