Author Topic: 1-Wire ADC chip  (Read 482 times)

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Offline RobBarter

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1-Wire ADC chip
« on: March 07, 2018, 04:07:12 am »
Hi

I'll put this in the beginner section as I am one :)

I need to measure a couple of voltages (1-5V) 100ft up a mast (approx. 50m cable length).  There is already a temp sensor (DS18B20) up there, or will be once I've assembled it, so was looking to add two ADC channels on a 1-Wire bus back down to the ground to measure FWD and REV power.  However, the only device I can find is a MAXIM DS2450 but that is discontinued although available from China and several weeks delivery.

In my searches the MAXIM DS2438 came up but it isn't very good at measuring below 1.5V.  It was designed for Li batteries.
Also found a BAE0910 but at £10 each (I need min 2) puts it above the cost of an Arduino.

The Arduino would be fine but it will be sitting approx. 10cm from a 300W 1296MHz RF amp and I'm a little concerned at it being effected by the RF or, more importantly, it effecting the pre-amp next to it.  It will also more wires down and probably require something like an RS485 line driver at each end.  However, it does mean I can add other stuff later.

Any thoughts as route to go or any 1-Wire adc's I'm missing?

Cheers
Rob
 

Offline tpowell1830

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Re: 1-Wire ADC chip
« Reply #1 on: March 07, 2018, 04:41:47 am »
Sorry, I am not familiar with those chips. I don't know anything about your project but LoRaWan is very useful for remote sensor measurements.

Check out Marco Reps' video:



There are many other videos about LoRaWan as well, just do a YT search.

Hope this helps...
PEACE===>T
 

Offline RobBarter

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Re: 1-Wire ADC chip
« Reply #2 on: March 07, 2018, 04:47:13 am »
Thanks tpowell,

I actually have a LoRaWan gateway setup at home.  A Raspberry Pi with IMST iC880A.  However, would not like to put a 868MHz transmitter right next to a very sensitive preamp for 1296Mhz.  It's a Ham Radio competition system.

Thanks for the suggestion though.

Rob.
 

Online Ian.M

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Re: 1-Wire ADC chip
« Reply #3 on: March 07, 2018, 04:54:52 am »
Although any small MCU could be programmed to operate as a 1-Wire compatible slave, or you could try to source N.O.S. DS2450 ADCs, IMHO you'd be crazy to do so.  With a high power UHF TX amp in close proximity, that's just asking for trouble.  Even the DS18B20 is likely to misbehave unless it and the bus feeding it are fully screened.

You'd be better off biting the bullet and designing a RS-485 based solution with a MCU in a fully screened box with feedthrough caps for power, data and any sensor wires and using resistive analog temperature sensors that wont misbehave with a stray RF field.  At 1285MHz, a quarterwave is only 5.8cm so if the screening box has a removable lid, it will need conductive fingers at less than 6mm spacing, or a copper braid or high conductivity elastomer crush gasket to get sufficient screening integrity - alternatives would be soldering the lid on or covering the seam with copper foil tape with conductive adhesive.
 

Offline RobBarter

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Re: 1-Wire ADC chip
« Reply #4 on: March 07, 2018, 06:06:54 am »
The DS18B20 comes already fitted to the copper spreader of the commercial 300W amp.  I'll tell you later how that goes :)
 

Offline Inverted18650

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Re: 1-Wire ADC chip
« Reply #5 on: March 07, 2018, 11:05:15 am »
off topic. Is the creator "Marco Reps" here on the blog? I've been binge watching his videos today and would I'd like to send him some toys to play with. Love his video style and share the Keithley passion.
 

Offline Kalvin

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Re: 1-Wire ADC chip
« Reply #6 on: March 07, 2018, 05:46:20 pm »
Not sure whether this is useful for this particular application, but you can also use Arduino as a 1-wire slave. Just google with following terms: arduino 1-wire slave
 
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Offline Cliff Matthews

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Re: 1-Wire ADC chip
« Reply #7 on: March 07, 2018, 11:33:29 pm »
off topic. Is the creator "Marco Reps" here on the blog? I've been binge watching his videos today and would I'd like to send him some toys to play with. Love his video style and share the Keithley passion.
Yes he's here as user "baltersice" but his channel now seems to be deleted from our YouTubers list (I'll notify Roger EZ24).
http://www.eevblog.com/forum/other-blog-specific/a/msg1352598/#msg1352598
 
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Online David Hess

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Re: 1-Wire ADC chip
« Reply #8 on: March 08, 2018, 05:19:52 am »
Since you are already sharing a ground with the 300 watt transmitter to measure the forward and reflection signals, I would use the same power or use a single point ground at the top of the mast to power a microcontroller like an Arduino to make the 1-wire measurement and any other measurements.  For communications, I would use 3 wire asynchronous serial with a pair of optocouplers at the bottom of the mast or wherever the RF and power lines terminate.

You will just have to deal with any interference from the RF transmitter.  This would exist whether you used a 1-wire ADC or not and attaching the ADC to the transmitter defeats having separate grounds anyway leading to more problems.
 

Offline RobBarter

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Re: 1-Wire ADC chip
« Reply #9 on: March 08, 2018, 06:10:33 am »
Thanks David

Looking more towards an Arduino at the top of the mast (I can put it in a tin to help) and keeping the earths separate from the bottom of the mast.  Good point on the opto couplers.
 

Online David Hess

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Re: 1-Wire ADC chip
« Reply #10 on: March 08, 2018, 06:24:49 am »
Looking more towards an Arduino at the top of the mast (I can put it in a tin to help) and keeping the earths separate from the bottom of the mast.  Good point on the opto couplers.

If I was not clear, that is what I am suggesting; put the Arduino at the top of the mast.

I would not rely on a non-isolated differential communications link going that far when a variable 300 watt load is at the end which shares a ground with the low level forward and reverse signals.  Maybe the power amplifier includes isolation for those signals but you did not say and even if it did, I would still use galvanic isolation on the communications link.  Optocouplers at the bottom of the mast are just the easiest moderately effective way to do that.

Note that both optocouplers go at the bottom of the mast or where the power and RF terminate because if they were at the top, coupling between the signal cable and RF/power cable would reduce their effectiveness.
 

Offline RobBarter

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Re: 1-Wire ADC chip
« Reply #11 on: March 08, 2018, 07:40:07 pm »
Definitely clear.  My comment "Looking more towards an Arduino at the top of the mast" was because of your comments and my own thoughts.  Acknowledging Ian's comment, I may put it in a tin enclosure.

I'll keep the thread updated as to how it goes.  The transverter is already built for the bottom end (which can drive two separate antenna systems/PAs) although the wiring needs a little tidying.
 


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