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Forum Index : Electronics : Remote Sensing
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi interested readers, I have been developing a Buck/Boost MPPT for use with Wind, hydro,or solar generator systems. Mainly though for the wind generator as this system has the most varied output voltage range. As a result of a need to accurately measure voltages at many different earth references I had to develop an isolated general purpose linear high resolution voltage coupler. I am looking at using a 433MHz transmitter/receiver pair to digitally transfer the signal, as a substitute for the opto coupler I am currently using, for applications where the measured variable is quite a distance from the control cct. Have any readers had experience with this type of radio equipment. With the trend to multi phase mills and capacitors, many readers would consider placing the rectifyer on the mill as well and only bring DC down the slip rings. In this application there may be a requirement to measure the AC waveform in operation etc. The remoote sensing cct would transmit the measured signal to the receiver. A multimeter could be used to display the changing signal in real time. This signal could be logged or used for control purposes. The quality would be similar to using the multimeter or CRO directly connected but without the need to be up the pole. The wireless weather stations have a prorietry coded data system that is not general purpose. I can see many other applications for this type of cct. Cheers, Gordon. become more energy aware |
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Bryan1 Guru  Joined: 22/02/2006 Location: AustraliaPosts: 1210 |
Hi gordon, ya might want to checkout the oatley website as they have some cheap wireless transmitters and recievers. Then go checkout Stan's NZ website as he has done some picaxe articles in the sillychip mag and he put everything on his website I believe Cheers Bryan |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Bryan, who is Stan ?? I assume you mean Silicon chip magazine. I have seen the oatley RF modules and they look promising. Same price as ones from JayCar. The Schotkey diodes and mosfets look promising as well. cheers Gordon. become more energy aware |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1210 |
So Gordon your into picaxe's and aint seen this site. On this forum Stan is known as Manuka off memory. Cheers Bryan |
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Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Gordon, Stan's the Man when it comes to PICAXEs. He has a few projects listed on his site that might be right up your alley. Check him out HERE This One especially? was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Bryan, Thanks for that info. I have only been involved with picaxe for a bit over a month, so I am no expert. cheers, Gordon. become more energy aware |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Gill, I do not intend to transmit data. I run the AXE08M at the maximum output rate for 10 bit transmission resolution. For control purposes my prototype updates the PWM signal at the maximum 2kHz[0.5mS]. I can now effectively transmit a 50Hz analogue sinewave, with 10bit resolution of the actual voltage. This is not data, or a coded representation. The structure of the signal retains the actual voltage. I have ordered a pair of TX/RX modules and will do some testing. The range of these devices has been reported at over 1km. I am hoping that the TX/RX pair can be operated at the maximum 10kHz rate. One application I was intending was to measure the current and voltage of my main solar array, without having to run any connecting wires. The array operates at up to 190V and the positive is at earth potential. I am interested to monitor the effect of the edge effect of cloud cover on panel output. I masured an incident solar radiation of over 1,600W/m2 last week. Anyway at the moment, the MPPT only needs to use opto coupling. Must get back to the coal face. cheers, Gordon. become more energy aware |
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| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Very much at a loss as to what you are trying to do and the way you are doing it. Seems a backward step to be transmitting in analogue with all it's vulnerabilities to RFI. That you have a 10bit resolution of the received signal is not unexpected, but what is the accuracy of the received signal compared to the transmitted signal over the intended distance? I would have thought a remote 08M and a TX434A sending data a better way to go. Using high gain antennas and/or repeater for longer distances. Still you seem to know what you're doing. Sounds like an interesting project.  was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Gill, this project will have a wide range of applications. I still have to finish my prototypes. I am currrently awaiting delivery of hall effect current sensors, [I may need to resort to a current shunt after all], and RX/TX units. however, with regard to some comments you made. At no time have I said I would be transmitting analogue signals. There is digital transmission and digital data transmission. My signals are still digital ON/OFF pulses, but there is no code transmitted. The information transferred [within the tolerances of the micro] is an exact representation of the source signal. There is only the transmission delay time, probably only nanoseconds.[I can accept this] I have used the concept in the past to transmit audio signals in a digital format with an audio bandwidth from 5Hz up to 50kHz [well below and above what I can hear]. I think you are being confused with my example 50hz sinewave. This statement I made is perfectly correct. The last sentence does state what happens. This does not mean the signal is analogue during transmission. I do not intend to reveal exactly what I am doing here. I have designed a prototype and I intend to show a CRO display of the simultaneous input and output. For the sceptics, I will also compare various types of data transmission with the digital approach I use as well. I will be able to reprogram the picaxe chips as each chip has an individual programming port. I have looked at the encoder/decoder example you gave in the link above. The processor overhead is significant. At 300baud, 64 bits are transmitted. A lot are used for the handshaking so you don't get garbage. I think 54 bits are used in this way. The system I intend to impliment will give an output digital stream at 8kHz that will be updated every 4th pulse. This will mean the new signal will be updated 2000 times per second. The example link above will, with the delays removed produce an updated output at a maximum 4.7 times per second. For control purposes, 2000 times per second is much more acceptable. I think you will see that this topic was a spinoff from the control loop in my MPPT, where update speed is paramount with a rapidly changing variable like mill output voltage in gusty conditions. The measurement of temperature is traditionally a very slow process. Update rates of minutes are acceptable. [unless you need to measure the temperature drop of product in a blast freezer]. At the end of the day, the TX/RX modules can pass 10kHz signals, so they will be fast enough. I may have to restrict the resolution to 2^10-2 instead of 2^10 for reliability, but this in no big deal. The transfer will still be linear in between though. The main limitation I can see is channel differentiation. From what I have read, all the devices operate on the same frequency. The RX module looks for a frequency within a range and then PLL's to lock the RX to it. Does anyone know if this is true. This will limit the use to only the measurement of a single channel with a radio link. I may be able to encode an identification signal to allow a greater number of channels. I do not really want to have to encode a TX to a matched RX module though. I hope to post some examples soon. cheers, Gordon. become more energy aware |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Gordon, When I needed to switch a pump on/off and all I had was an electrified fence running for 300 m, I received a lot of help from Dr_Acula. It may have been on this forum or Otherpower. He has even come up with coding systems for the data comms to be more foolproof and he is using Picaxes for his wireless transmissions. Go, get it! Regards, Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Gordon, The site may have been the main Picaxe site and not this forum or Otherpower. Sorry! Regards, Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Thanks domwild, I have had no success finding him with google, or dogpile search engines and have searched this site and otherpower. I have seached for PICaxe and 433MHz RX/TX generally on the net. The only info I have found is related to tasks that are not time critical. The applications are where security coding or data transfer is required. I will have my new PCB's done by next week and hopefully Oatley wil have sent my TX/RX pair as well. I will post my results, if it works or not. I have a 4 channel CRO, so I will be able to show analogue in, digital to TX and RX digital and analogue out, all on the same display. You mention Comms being more foolproof. This usually means error checking or checksums to confirm correct data transmission. This may be important if you need to open the right door, etc. From the lack of any posts on how well these devices work, I have to assume they work perfectly. I will find out when I get to test mine. cheers, Gordon. become more energy aware |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Gordon, Sorry, checked my files and it looks like I did not save his three schematics. Will have a look for you in my papers and might be lucky. Regards, Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Gordon, Feel a real dill because I could not help you, however, a very helpful person is Dr_Acula (moxhamj at internode dot on dot net) He sent me three schematics of transferring data over wires if I remember clearly but also uses wireless transmissions. Not that you need much help judging by your contributions, but I am sure this academic (from memory) will gladly help you. Regards, Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Dom, I now have a pair of the 433MHz TX/RX devices. I hope to make a start this weekend. cheers, Gordon. become more energy aware |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi all interested readers. I have tested using pwmout, pulsout and serout communication. The 433MHz pair is unsuitable for PWM coupling, even at 4kHz, the minimum modulation frequency of the AXE-08M. The devices are able to transfer digital signals with the pulsout command at a speed of 500 readings per second. The serout command is useful for transferring small packets of data at a fairly slow rate at a maximum 2400 baud using an AXE-08M. This equates to approx 120bytes per second if the AXE-08M does nothing else. For maximum speed the data should be transfered in binary. This is primarily the use, other experimenters have toyed with. eg silicon chip article. Character 170 digital should be sent in binary [10101010] to establish communication. The use of padding characters does reduce the bandwidth available for the actual data. The pulsout/pulsin commands provide the fastest digital transfer using the 433MHz TX/RX pair. A zero offset, is required to eliminate noise from the receiver output at a zero input signal. This is related to a step signal that remains on the receiver when the minimal signal is transmitted. The 500 readings per second allows a moderate system control rate. The AXE-08M, pulsin command will measure the pulse length, but this will still need to be converted to a useful form for control purposes. I will test the pulsout type transfer on my mill. I have the rectifier on the mill head. Hopefully, this radio link will enable me to display the mill output waveform and allow frequency and hence rotor rpm to be measured on an isolated live mill. A multitude of calculations would then be possible with this additional information. I still have some more things to try. cheers, Gordon. become more energy aware |
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| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Sounds like it'd be great for logging masthead data. Must get a pair when things quiten down and I've got some time to play. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi All, Just an update. During my testing of the 433MHz pair, I have seen the poor quality of the digital transfer between the devices. I found that in a noisy environment the receiving chip may take an ordinarily long time to receive the correct code string. If one was trying to log this data, then logging errors would creep into the data set. My system eliminates this. I have found that my method of information transfer allows simple post filtering of the information. The filtered analogue signal can then be re digitized and then logged etc. The receiving AXE-08M micro first converts the incoming data pulse stream from a time value to an equivalent linear voltage representation. This is then filtered and re sampled by an A/D input. This is all after the RF link. Any noise during transmission seems to be easily filtered, leaving behind the correct analogue voltage. The basic system is an analogue in and analogue out linear digital transfer. I have restricted the analogue input to 50V Max. This will correspond to a 5V output. Input resolution is of course 50mV. This will be more than adequate for most measurement applications. I will start some transmission range tests soon. cheers, Gordon. become more energy aware |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
[Quote]Any noise during transmission seems to be easily filtered, leaving behind the correct analogue voltage. By reducing the data through-put. Take an noisy digital system, sample the signal say 5-10 times and take the most frequent answer (which still might not be correct). Problem is data through-put has been reduced by 5-10 as well. This may not be important in your system. What is causing the noise? Poor signal to noise ratio caused by a deaf receiver, a low power transmitter or poor antenna design. Or is the noise being generated in the unit itself? [Quote]The receiving AXE-08M micro first converts the incoming data pulse stream from a time value to an equivalent linear voltage representation. I would expect any noise on a digital signal, that leads to incorrect detection would not be a worthwhile contribution towards any "averaging" process. What bit rate and modulation format do these modules use? If data integrity is important then some form of ACK/NAK signalling if needed to ensure that the receiver got the correct answer, see checksum and CRC as in Xmodem, etc. Sending the same data , say 5 times and the receiver saying I received the <same> answer 3 times out of 5 does give you some confidence that you got the right answer. Dave |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi dave, what you have stated is quite valid for a much more powerful micro, but the options are very limited with only 14 bytes or 7 word variables in an AXE-08M. cheers, Gordon. become more energy aware |
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