wireless transmitting

You certainly can send the data over 20 m of wire - there's no technical reason why you can't anyway.

Why not send it down a wire?

RS232 should cope with that length of copper and its much cheaper and reliable than having a radio link.

John.

Use signal transmitter similar to 4-20mA or frequency based such that information can reach on two wires / 3 wires up to 20m away. This may be possible within US$200 to US$300 including a sensor for up to 3m depth. If accuracy requirement is not very high then a capacitive sensor looks OK and you can get frequency output to be counted in your uC and you can display it. Other alternative is pressure sensor, which may be a bit expensive to US$500 range if taken from professionals such as www.globalw.com or HOBO series water level sensor. These sensors go under water.

Another possibility is to look at water from top and measure the distance using ultrasonic echo sensor. This can measure up to few meter changes easily with cm accuracy and can come for US$300 range. Look for www.banner.com and www.turck.com links.

You can also look at www.automationdirect.com/ and few more automation sensors manufacturer's web sites.

Sending the signal down a wire would be the simplest solution considering the fact that the sensor is going to require power of some sort to operate and therefore will have wires running to it anyway.

Having said that I would not suggest hanging a 20 m long piece of wire directly of the input line of a PIC microcontroller. A 20 m piece of wire is going to act like an antenna and the input impedance or the input lines on a PIC microcontroller is high enough to cause problems. You may even damage the chip in the event of a sudden spike being induced on the cable as well. I would suggest using an opto-isolator or something similar at the microcontroller end of the circuit.

While it is possible to do it with a radio transmitter and receiver the cheaper and more reliable option would be a cable from the control board that not only carried the power for the sensor but the return signal.

Dear Mark

That is like a real engineer giving nice piece of advice. I agree with your points and even if such designs are for hobby, they need some care to get a reasonably working model. One easily comes across the voltage drop in the signal line and the ground reference no longer remains the ground level signal. Hence use of an opto-isolator is a very good idea.

By the way, what is that on the top of your icon the blue with Red eyes? Is it a bird or a hat? Why your flag is below the icon? I thought it should be above all things as it represents a nation. You can sit on your instruments but can't do so for your flag. Perhaps that bird can hold your Flag. John has also placed his British flag below his icon. It is disturbing my thoughts by looking at that way. Putting flags on dress may be OK but not to be placed below a person or whatever. Never mind if you like it that way. Perhaps the Flag and the instruments are on display in front of your icon, which is behind the seen as representative. That may be considered OK. John's icon look like that, but not your icon.

Hi Shyam,

The little bits sticking up are the two or three hairs that I have left on my head after puling them out in frustration. Actually I have hair that sticks up just like this when I get up in the morning.

As for the flags they aren't part of the avatar, they are separate icons that represent membership of user groups. The flag means I am a member of the Australian user group while the thing in the right is the Fans of Old Computers group and shows a Honeywell H-316 which was the first computer that I really got inside.

If you go to your membership profile you can join any user groups you wish.

Dear Mark

One of my colleague was always twisting his hairs as he comes from silk manufacturer family where he was to remove silk by twisting the yearn. Even though he came a physicist in the atomic energy, he continued twisting something or the other and his hair came handy. He twisted that many hairs that he had a desert on his head. Your joke about your hair is interesting one and I learnt from you about the extra icons that you have. I added the name of the place with my identity as people used to believe I am from Korea. My knowledge about Korea is only limited to one atomic energy engineer Kim who came for one UNO meeting with me in Dominican Republic. He said that after his graduation he spent 3 years cleaning gun barrel as defense service was compulsory. I am very restless and can't spend even one hour in the barber saloon so go only once a year. By then my hair grow 12" and my wife and children start offering money for hair cut. My hair grow 1" each month and now these are about 10" I suppose so another 2 months to go for haircut unless I miss the date.

There is one company in India which makes 15 million dollars years by reprocessing hair. If all Indians donate hair then it should become a billion dollar industry. That much to hair and hair raising experiences. Hair carry history of toxic intake in them in length and are good way to analysis the average problem of the place. Many metallic elements are part of the air.

It is very interesting to show hair in that shape. I will call it wonderful. I am somehow scared of those red eyes, which you hold all the time and the blue is OK for Indians as Lord Krishna was blue and Lord Shiva is Blue Sky for me.

What sensor are you using? Or am I correct in assuming you don't have a sensor yet? You did say, i want to... so I guess you haven't made a choice yet. You also seem to have limited yourself to using a PIC with a low voltage input. Okay, so here goes.

You can buy several types of level sensor or you can make them yourself. One that comes to mind is a float connected to a potentiometer so that it changes the resistance as the level changes. How to get this signal to the PIC which is 20 meters away?

Sending the signal as a voltage is asking for trouble. The wire, as masu says, can act like an antenna. So if you don't want Britney Spears giving you your level, I wouldn't use voltage.

The simplest thing that comes to mind is to inject a constant current down through the wire. That current passes through your potentiometer and through another resistor near the input of your PIC. The current is converted to a voltage and you have your signal. How you connect your float to the potentiometer is up to you.

Just remember to use shielded, twisted wire. The 10mA is just a suggestion. You can make your own calculations to find the values for current and resistance.

Firstly you are going to cause a whole lot of confusion---You pinched my avatar!

PleaseChange to something else!

Secondly Wireless transmission is already highly practiced in large plant (and wired home)--Instrumentation/Telemetry/Telecontrol.

Are you sure you would like to spend $10,000 on a wireless system-- instead of $10 on a 20m long multicore control cable?

Hello Mukulmahant

I think some $200 wireless technology may be possible to satisfy the ego of small level inventors. I have seen some of these at www.radiometrix.com/ and these things work fine up to 100m for 10mW power. Data on air is a fun.

For 10m perhaps a sound beacon may also work. Put a small speaker and receive a sound of a frequency. Perhaps ultrasound link is also possible but audible sound will be cheap. 40kHz air transducers may cost only US$10 and here one goes wireless.

Small solar cell can power the transmitter then power should not be a problem. Why to discourage the idea of not using wireless?

Hi...

It's better to convert the signal from electrical signal into light signal so that you can use a fiber optic to transmitt your data over a long distance.. At the other end, you must have a device capable to receive and interpret the light signal and convert it back into electrical signal so that it can be interpreted by your microprocessor...

This is RICHARD BARCELO, ELECTRONICS TECH.

I agree with Richard that data can be transmitted using modulated IR up to 20m easily but requires a line of site view.

Hi..

yes it's true, by the use of light signal instead of electrical signal, you can avoid electrical interference generated by the copper or conductive wiring's. Use fiber optics cable to send your data into control room. Transmitt the data signal by converting it first into light signal using electrical to light signal converter, now the output is a IR signal and you can now coupled it to the fiber optics cable and run it into the control room, the light to electrical signal device here should be used to accept the received light data and convert it back to electric signal that the microprocessor can accept and interpret the data signal..

Fiber is again a wired system.

I have no objection to people trying out new technology. I've done that a lot myself. However, there are certain areas where simplicity is best.

For a wireless system, you need to provide power to your transmitter. That's an additional item. You can use solar cells, wind power, maybe even multiple thermocouples (I'd like to see someone try that!). Just a little lower on the technology side is to use long life batteries.

Your transmitter can be radio frequency, ultrasonic (difficult if the sound has to travel 20m in open air), laser (line-of-sight) or infrared (again, line-of-sight but more forgiving than laser). Each type has its own advantages and disadvantages. Whatever your technology, you need to convert your raw signal to voltage to interface with your PIC.

It's nice to tell your client that he can have a water tank 20m away and doesn't need wires to send the level signal to the house. If he loses the signal, however, troubleshooting will have to be done and the more complex or sophisticated it is, the more difficult and more costly it will be to fix.

'Ever hear the adage, "what you want is not necessarily what you need."

If Transmitter is used in switched mode then data is transmitted every 1 minute at about 9600 baud only few characters may result into small power and a Lithium battery may work for years. Perhaps a Low battery signal can also be transmitted.

I built one for capacitive / resistive sensors and published in Electronics Design magazine. This design changes the base frequency and not modulation.

http://www.elecdesign.com/Articles/ArticleID/3503/3503.html

Single-Gate VHF Temperature Transmitter Runs On 3.6 V

Shyam Sunder Tiwari | ED Online ID #3503 | December 3, 2001

This design idea illustrates what may be the simplest and smallest temperature transmitter in the VHF 50- to 100-MHz range. As seen in the figure, the design employs an ON SEMI single-gate IC (NL27WZ14). The sensor is a negative-temperature-coefficient 1-kΩ SMD thermistor. It causes an increase in the oscillator frequency as temperature increases. Since the design of the circuit is not critical, the value of C1 can be selected high enough to lower the transmission-frequency band down to 1 MHz if necessary. The thermistor-resistance value, however, is critical and should not exceed 3 kΩ. If the resistance value exceeds this limit, the circuit may not oscillate properly.

The data is transmitted as a slowly modulated FM signal (i.e., the frequency shifts as temperature changes). Therefore, rapid signal modulations, typical in audio FM receiver systems, are not involved in this design. At the receive end, the receiver locks on to the transmission frequency and monitors the frequency variation directly as the temperature signal. C1 must not have a positive temperature coefficient or frequency compensation will be required to cancel the temperature dependency in the R1C1 time constant.

To limit the size of the transmitter, a small wire hanging from the tiny pc board is used as the antenna. Other types of antennas may also be used.

Since this circuit draws less than 10 mA from a NiCd cell, its operating time with a small cell is reasonably high (i.e., a few days). Power can also be supplied from other types of cells in the 3- to 5-V dc range.

Hi Shyam,

Nice circuit, well thought out. However, different people, different experiences, different opinions.

Though the OP wants to use wireless, I did not offer a wireless solution. The method I posted is simple, inexpensive, easy to build, install or troubleshoot, and it works. I have no doubt that your solution, as well as the others, would work. I just don't think it's necessary to be more complicated or sophisticated than what I offered.

Of course, our OP can make his own choice. All we can do is suggest.

This circuit type was also built for fiber optic transmitter and published in Electronics Design. I have more than 600 such designs to my credit. You can replace the HS1101 humidity sensor with capacitor type water level sensors.

This was published in 2002 in Electronics Design. See link below.

http://www.elecdesign.com/Articles/ArticleID/1684/1684.html

Simple Circuit Uses Optical Fiber To Send Relative-Humidity Data

Shyam Sunder Tiwari | ED Online ID #1684 | April 01, 2002

The circuit shown in the figure measures relative humidity in air at the low temperatures found in applications like cold storage of food items and greenhouses. Instead of using electrical signal cables that are rated for such harsh environments, the design transmits its signal on low-cost, plastic optical fibers.

This design uses an HS1101 relative-humidity sensor from Humirel (www.humirel.com). The sensor acts as a capacitor (C1) whose value varies from 180 to 220 pF for relative humidity in the range of 0% to 100%. The sensor is linear within ±3% of full scale.

A Motorola NL27WZ14 single gate is implemented as a free-running oscillator. The time constant, (R1 + R2) × C1, sets the frequency of oscillation. The output from the oscillator goes to the 2N2222 transistor, which drives the LED to flash the light into the optical fiber. The duty cycle is nearly 50%, which cuts the power drawn by the LED in half. A 3.0- to 3.6-V battery can power the circuit. If a NiCd battery is used, it can be charged by a wall adapter. But in place of the battery or cells, a 5-V regulated power supply can be used.

Note that the HS1101 sensor is slightly nonlinear with respect to temperature. However, this isn't a serious problem in the above applications where temperature is generally regulated and humidity is controlled.

Relative humidity is computed by measuring the received signal's frequency through the optical fiber via a photo diode. There's a baseline reading due to the minimum capacitor value at 0% relative humidity. This must be subtracted from the frequency reading to get the correct percentage for a 0% to 100% range. Results were within a ±5% limit for 10 tested sensors. Over 10 readings, the average was within ±3%.

I'm not familiar with the NL27WZ14. How's the stability of the frequency with respect to temperature?

If it's anything like a typical CMOS gate, you need to have a good, steady supply voltage on it. The frequency is affected by variations in the supply voltage. Temperature is also a problem as some components drift with temperature. Of course, you could use a 12V battery and use a regulator or zener to drop it to 3.6V. That way, even if the battery drops to 5 or 6 volts, it will still operate.

Alternatively try TLC555 of Texas Instruments which is very stable for oscillator design. LMC555 may also be good. Frequency is not affected as output voltage and threshold levels change in same proportion to power source. TLC555 will work from 5V to 12V range power. Hence, 9V battery can make it operate for long period using 1M Ohms timing resistor and 50% duty cycle and limited drive current.

I read your post and wanted to share with you our 4-20ma wireless system. We have system that can go up to 5 miles. The nice thing about wireless is that you don't have to trench to lay wire. You can view this system at our website www.remotecontroltech.com.

make it simple!!!

20 metters wire is the easiest.

Next easiest will be to buy a 5USDlls wireless car and take the radio system from it... what?.. I did it before.

Saludos!

buy a 5USDlls wireless car and take the radio system from it

i dont know what that is

please tell me about it

if you can send me a link or data cheat it would be great

http://cgi.ebay.com/RADIO-CONTROL-STUNT-VEHICLE-SPINNING-ACTION-SILVER-NR_W0QQitemZ120089625279QQihZ002QQcategoryZ1200QQrdZ1QQcmdZViewItem