ADC reading through wire from a Distance ?

picaxe 08m adc

Hi

I have to read the position of a potentiometer shaft from a distance.

The potentiometer is placed 150 to 200 meters from the control room. The supply voltage is 24Volts DC.
I have to report the position of potentiometer in the control room.

The display and other methods I have an idea. But will the normal ADC reading method will work in this case. The potentiometer one end to +24 volt other end to gnd and centre point to ADC input.

What is the best method for my purpose.

please suggest


picstudent

08m picaxe 433mhz

Hi

Use 4-20 mA current TX technic to trnsfer ADC data from remot location - you will need only 2 wire

Other methode involve converting the ADC result to Digital data and transmit them using sync or Async communication methode with a low cost microcontroller

All the best

Bobi

wikepedia sn75176

Thanks a lot for the response

Use 4-20 mA current TX technic to trnsfer ADC data from remot location - you will need only 2 wire

Click to expand...

can you little more eloborate on the details. What is this Current Tx method?

Other methode involve converting the ADC result to Digital data and transmit them using sync or Async communication methode with a low cost microcontroller

Click to expand...

This thing I understood. By using serial port of PIC (or any MCU) and max 232.

But can we transmit upto 200 meters using Max 232 on both sides?

Thanks again

picstudent

sn75176 with pic addressing

Use 4-20 mA current TX technic to trnsfer ADC data from remot location - you will need only 2 wire

Click to expand...

can you little more eloborate on the details. What is this Current Tx method?

Click to expand...

Check these articles:
:arrow:4-20 mA - Wikipedia, the free encyclopedia
:arrow:4-20 mA Current Loop Primer
:arrow:Analog Inputs - 4-20 mA Transmitters
:arrow:ANALOG DEVICES AN-21 4-20 mA Digital to Process Current Transmitter

10 bit adc reading

Hi
Thanks a lot.

Got the idea. IMplimenting it seems a tough task for me.

any readymade transmitter and receiver modules availble?

Costly?

Thanks again for the links

picstudent

Depending on the circumstances you can also consider other option(s) ..

If it is possible, you may use PICAXE-08M ($3) and el-cheapo RF 433MHz transmitter ($5) at the potentiometer end, and matching RF-receiver at the other end, so data comes in serial format, something like RS-232 but in TTL/CMOS levels - no MAX232 required ..

Why PICAXE? The PICAXE-08 has 10-bit ADC and is extremaly easy to program in BASIC ..
See this topic:


As far as 4-20mA off-the-shelf solutions are concerned, take a look at the XTR110 (or others from this series) ..
https://focus.ti.com/docs/prod/folders/print/xtr110.html
This may be not the cheapest solution ..
Here is another option (4-20mA, also based on PICAXE µC):



Regards,
IanP

A pot divider, A PIC and 433Mhz RF TxRx pair would just be what the doc ordered..

What do you guys think ?

If you'll live in the 80' I'll vote too for 4-20mA curent loop, that was the most used methode in that time.
Nowaday's the technology changed everything. The less perturbed methode is
transforming the AD signal it in logic signal and send it to a line.

So the way is do it in 2007 is:
analogic signal-A2Dmicrocontroller-communication path-microcontroller-display

Despite the lenght of the above chain it's not expensive at all.

TX: 10 bit ADC, PIC12F675 using bitbanged usart to RS485,
RX: RS485 to RS232 converter + PC for display and analyses (or other microcontroller)

Yes... my point exactly. For low quantity a PIC16F877A with hardware USART would not be too much of a financial problem

If you want to monitor if for a long distance you can try the idea i found on the net.

Use an ethernet to serial converter.

First convert the potentiometer readout to digital using MCU. Send the digital readout to the serial web server. Your data is now available on the net and can be accessed any where.

This is just an idea.

A RS485 solutions would be more than enough and cheaper both on the pocket and code...

Ethernet seems too much for something so little.

Hi

Thank you very much for all suggessions.

RF link I am not sure because this thing is to be deployed in a fishing vessel.
(Not a titanic, smaller )

will RF transmitters like this(433Mhz RF TxRx pair) reliable on a matalic structure like boats and ships?

My preference is for RS 485 from the opinions above.

Let me search and collect more details to impliment a RS485 link for my purpose.
links are welcome.

Thanks a lot again.

PIcstudent

Later..

We can impliment this circuit using Sn75176 (available cheep locally! ) right?

Then what is the extra benift if we use MAX485?

As i understand

transmitting side(slave) Potentiometer , PIC with ADC and USART, and SN75176,

receiver side(Master) - SN75176, PIC with USART and display or whatever.

PIC in the control room( , Master - enables transmition of 75176 and send a packet with command and data if required. and disables transmition and waits for response.

Receiving slave PIC always in receive mode of 75176 . When its usart receives a packet checks the command in the packet , takes the appropriate data, enables transmition to 75176 and sends the desponse packet and returns to receive mode.

So the use of 75176 in my case will be only to derive this 485 differential bus. (No addressing or multi Node in my case)

Also the only change from normal USART code in PIC will be a special enable disable transmition pin control. Am I right?

Any schematics?
What will be the advisable baud rate for my purpose?

Thanks

picstudent

The MAX485 is atleast 5 times more expensive, right ?



It's because you can string more than 16 devices because of it's better capacitance/long wire driving ability and switching characteristics..

Plus it has +ESD Protection.