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Optical wattmeter for £10

Sam Sung 1959 23
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  • Optical wattmeter for £10 .
    I prove that it is possible to measure instantaneous power and watt-hours consumed with the cheapest bicycle meter, a phototransistor and a resistor :)
    You only need to:
    - take the plus battery out of the meter
    - cut the reed switch from the cable and identify which of the two wires is the minus of the battery
    - connect the emitter of the phototransistor to minus and the collector to the return wire
    - connect a resistor between the positive and the collector of the photo transistor
    - connect the phototransistor to the LED in the energy meter
    I used a Shenb SB-318 counter ($2), a FT06-M phototransistor (£1.20) and a 10kΩ resistor.
    Optical wattmeter for £10 Optical wattmeter for £10 Optical wattmeter for £10 .
    And here's a video showing how it works when an approximately two-kilowatt kettle finishes boiling water:


    .
    The energy meter does 2,500 pulses per kilowatt hour, so I've set a circle circumference of 4,000 mm, so the result of 21.1 km/h means an intake of 2110 W.
    You can see that with each pulse, 4 metres of distance is gained, and the 1,580 km gained is 0.158 kWh.
    Unfortunately, the bike meter does not show speeds of less than ~3 km/h, which translates to 300 W. An energy meter doing more imp/kWh would have been better suited.
    Finally, I'm glad to have met @efi222's challenge from https://www.elektroda.pl/rtvforum/topic4067036.html#21167617 :) in less than a year.

    Cool? Ranking DIY
    About Author
    Sam Sung
    Level 33  
    Offline 
    Sam Sung wrote 1931 posts with rating 487, helped 225 times. Been with us since 2005 year.
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  • #2 21599763
    chudybyk
    Level 31  
    A small correction: a colleague did not make a wattmeter. This chip does not measure watts. It is at most an indicator of how fast a diode is pulsing. The fact that it was a diode from a wattmeter makes little difference. But the idea is quite funny.
  • #3 21599809
    speedy9
    Helpful for users  
    Interesting patent. But don't electronic meters show these values on the display? Another thing is that the meter can be reset and measure, for example, the daily energy consumption.
  • #4 21600281
    TechEkspert
    Editor  
    Not a bad imagination and it's a very out-of-the-box approach.

    I find it hard to imagine the reaction when someone hears the conversation:
    'the power consumption of this device reaches 5km/h, while during yesterday's day the power consumption was 200km.

    AI has no chance of understanding this thread :) .
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  • #5 21600284
    Sam Sung
    Level 33  
    chudybyk wrote:
    The fact that it was a diode from a wattmeter doesn't change much.
    In my opinion, it changes everything :) .
    chudybyk wrote:
    This fridge does not measure watts.
    The circuit consists of 2 components. A resistor polarises the phototransistor, and this converts the light pulses into short circuits. And that's as much as it does.
    And after connecting the circuit to a bicycle meter and gluing the phototransistor to a diode in the energy meter the whole thing measures watts :) .
    chudybyk wrote:
    Slight correction: a colleague did not make a wattmeter.
    If I connected a pair of pads together and got something that shows power in hundreds of watts, did I make a wattmeter or not? :) A subject for philosophers.
    Anyway, out of process precaution I called this thing a optical wattmeter , a non-existent term :) .
    speedy9 wrote:
    But don't electronic meters show these values on the display?
    I think I once saw a meter somewhere at someone's place that cycled a lot more parameters, including instantaneous power.
    I'd love to reconfigure what's showing there, but I don't know how <br/span>;) .
  • #6 21600318
    efi222
    Level 20  
    Congratulations on realising the idea :D .
    Sam Sung wrote:
    Finally, I'm delighted to have met @efi222's challenge in less than a year
    .
    I have to admit I'm surprised.... :)
  • #7 21600372
    mipix
    Level 38  
    You just forgot to add that these bike counters require the circumference of the wheel according to which they change their readings of speed and distance travelled. Have you thought about calibrating this somehow with the frequency of the light blinking?
  • #8 21600389
    p.kaczmarek2
    Moderator Smart Home  
    Fun and interesting, but a bit spoiled by the price of the bike meter - $2. For that much you can already get a WiFi programmable module with ESP8266 in China, and it is also very cheap in our country:
    Optical wattmeter for £10 .
    I would love to see the same project but just done this way - with WiFi access.


    PS: I had an identical counter for my bike.
    Helpful post? Buy me a coffee.
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  • #10 21600511
    speedy9
    Helpful for users  
    Sam Sung wrote:
    I think I once saw a meter somewhere at someone's place that cycled a lot more parameters, including instantaneous power.
    I'd love to reconfigure what's showing there, but I don't know how
    .

    Unfortunately, but it looks like what the meter displays depends on how it's configured: https://www.elektroda.pl/rtvforum/topic3656022.html
  • #11 21600682
    Sam Sung
    Level 33  
    mipix wrote:
    You just forgot to add that these bike counters require you to enter the circumference of the wheel according to which they change their speed and distance travelled readings.
    I did not forget:
    Sam Sung wrote:
    I set a wheel circumference of 4000 mm
    .
    mipix wrote:
    Have you thought about calibrating this somehow with the frequency of the light blinking?
    I calibrate it so that the kilometres correspond to a decimal multiple of the watts. The electric meter just happens to have 2500 imp/kWh. So I set wheel circumference = 4000 mm, which when multiplied gives 2500 imp/kWh * 4000 mm/imp = 10000000 mm/kWh = 10 km/kWh. From this, the meter shows 21.1 km/h (as in the video) when the power consumption is 2.11 kW and the distance of 1.58 km corresponds to 0.158 kWh. I could set myself a 400 mm circumference and then 1 km/h would correspond to as much as 1 kW. For measuring power this would be poor, but for counting energy consumed perhaps better.
    Worse if the meter has, for example, 6400 imp/kWh, because the fractional (1562.5 mm) circumference of the wheel cannot be set.

    By the way: when will you publish the access point resetter/restarter project you promised 20 years ago? :) .
    mipix wrote:
    full project coming soon
  • #12 21600889
    kris8888
    Level 39  
    These cheap bicycle counters have a relatively inaccurate internal (quartz) frequency reference. I infer this from the fact that I have two such counters and after a month they show a considerable deviation in the watch readings. Probably in the short term, for measuring bicycle speed or distance travelled, this does not matter much, but for such a long-term measurement of electricity, it can already introduce a certain error.
    It would certainly be possible to correct such an error precisely using, for example, the "wheel circumference" parameter, except that it must be compared with the readings of an energy meter with valid verification.

    Anyway, the idea is interesting.
  • #13 21600966
    Sam Sung
    Level 33  
    With this inaccurate time or there frequency standard it is true. The manufacturer does not specify the accuracy, because it is a toy and not a measuring instrument :) .
    But - the accuracy of the time measurement by the bike meter only affects the power measurement. The energy consumed (i.e. distance) is counted according to the number of pulses and this is not affected by the accuracy of the resonator.
    If we corrected the time lapse by changing the circumference of the wheel, we would simultaneously spoil the measurement of energy consumed.
    And without any correction, we have a measurement of the energy consumed with the same accuracy as an electric meter flashes, and an approximate measurement of the instantaneous power consumption.
  • #14 21601002
    kris8888
    Level 39  
    Sam Sung wrote:
    But - the accuracy of the time measurement by the bike counter only affects the power measurement. The energy consumed (i.e. distance) is counted according to the number of pulses and this is not affected by the accuracy of the resonator
    .
    Well, yes, you are right, the measurement of energy only involves adding a fixed number of units, derived from the value of the "circumference of the circle", every single pulse coming from the photodetector.
    Only this measurement of instantaneous power is affected by the accuracy of the meter's internal quartz resonator.
    That is, it appears that the only way to possibly improve the accuracy of this power measurement is to replace the watch quartz with some better, more accurate one. On the other hand, the super accuracy of such a wattmeter is not needed anyway.
  • #15 21601364
    chudybyk
    Level 31  
    The accuracy of the quartz is small beer.
    Maruda mode ON:
    1. it is not even a substitute for a wattmeter, because it does not indicate power, but energy/work. After all, a wattmeter indicates the instantaneous value in watts, not Wh.
    2. this instrument will indicate the energy consumption at some time interval for the entire circuit under which the meter hangs. And if I wanted to know how much the fridge would take in a 24-hour period.... then I'd have to have a separate energy meter, or unplug anything that might be drawing electricity for the duration of the 'measurement'. I would become an anti-hero in my house. ;-) .
    3. a Chinese dog-socket energy meter will almost always perform better, so I would treat this out-of-the-box solution as a curiosity.
    Maruda mode OFF.
    Despite the low usefulness of this mini project, I appreciate the creativity. Perhaps it would be possible to find an area where it could be applied, but I would like to see the face of the man from ZE who sees it installed on a beautifully sealed meter. :-D .
  • #16 21601493
    Sam Sung
    Level 33  
    chudybyk wrote:
    this is not even a substitute for a wattmeter, because it does not indicate power
    Not true :) Have you watched the video? I explained underneath it that:
    Sam Sung wrote:
    the result of 21.1 km/h means an intake of 2110 W.
    You can see that with each pulse, 4 metres of distance is gained, and the 1,580 km gained is 0.158 kWh.

    The bike meter indicates power (in hundreds of watts) and underneath energy/work (in tenths of a kilowatt hour - you may not be able to see it, but there is a dot before the 3rd digit from the end).
  • #17 21602364
    acctr
    Level 38  
    chudybyk wrote:
    this is not even a substitute for a wattmeter, as it does not indicate power, but energy/work. A wattmeter, after all, indicates the instantaneous value in watts, not in Wh.

    Unfounded fears, as everything is correct.
    A bicycle speedometer shows speed as the derivative of distance relative to time.
    Here it presents power as the derivative of energy relative to time.
    Helpful post? Buy me a coffee.
  • #18 21603734
    ACCel
    Level 22  
    I like the idea, if the author has established the circumference of the circle properly then the values will be correct, just the units strange :D
  • #19 21604163
    kris8888
    Level 39  
    Sam Sung wrote:
    The energy meter does 2,500 pulses per kilowatt hour, so I set a wheel circumference of 4,000 mm, so a result of 21.1 km/h means a consumption of 2110 watts.
    You can see that with each pulse, 4 metres of distance is gained, and the 1,580 km gained is 0.158 kWh.
    Unfortunately, the bike meter does not show speeds of less than ~3 km/h, which translates to 300 W. An energy meter doing more imp/kWh would be better suited.

    This bike meter, from what I can see in the manual, allows you to enter wheel circumference from 0mm all the way up to 9999mm. Have you perhaps checked what would happen if you entered twice the value relative to what you currently enter, i.e. 8000mm ? Admittedly, the indication of the distance corresponding to the power consumption would then have to be divided by two, but the indication of the speed, e.g. 3km/h, would already mean 150W of instantaneous power.
    Although I suspect that the limitation in these cycle counters, as far as minimum speed is concerned, is the maximum time interval between successive impulses from the sensor.

    Interestingly, my bike counter allows me to enter a maximum of 3999mm of wheel circumference, which I checked directly in its settings.
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  • #20 21605169
    szy0mon
    Level 1  
    I apologise to all those who have written here but out of curiosity I have carried out all the tests (by taping the meter from my daughter's bike) and unfortunately it is total nonsense . the fastest test is with a clamp meter preferably U type
  • #21 21605242
    jarek_lnx
    Level 43  
    kris8888 wrote:
    These cheap bicycle counters have a relatively inaccurate internal (quartz) frequency reference. I conclude this from the fact that I have two such counters and after a month they show a considerable deviation of the watch indication.
    Even an inaccurate, cheap, quartz clock, is more accurate than most instruments, in the workshop of the average electronics technician.

    An electricity meter, is unlikely to be as accurate as a cheap quartz clock Maybe some laboratory power/energy meter at the price of a car could compete in accuracy with a watch for a few zloty.

    Quote:
    I apologise to all who have written here but out of curiosity I have carried out all the tests (tapping the meter from my daughter's bike) and unfortunately it is total nonsense . the fastest test a clamp meter preferably U type
    A typical clamp meter does not measure power. Measuring from a meter has some small error but perfectly accurately determines what we will have to pay for
  • #22 21605412
    kris8888
    Level 39  
    jarek_lnx wrote:
    Even an inaccurate, cheap, quartz clock, is more accurate than most instruments, in the workshop of the average electronics technician
    .
    It depends on what such an average electronics technician actually has at his disposal, and it is not necessarily instruments at the price of a car.
    If one accepts indirect measurement of power as a derivative of pulse frequency (low frequency in this case) then here even any old frequency/pulse meter e.g. from Zopan, with OCXO as frequency standard, will give at least one order of magnitude better accuracy than that quartz watch built into a bicycle counter. The fact is, however, that not everyone has a decent frequency meter in their workshop.

    On the other hand, if one were to consider direct measurement of power as a product of voltage, current and cosine of the displacement angle, then even an ordinary analogue ferromagnetic wattmeter will also give slightly better accuracy than this bicycle meter, because power can be measured with the accuracy of individual watts.

    Of course, for simple and indirect measurement of power such a bicycle meter is almost ideal, even if it measures with a resolution of only up to 10W. With such a resolution, the accuracy of its internal quartz clock is irrelevant here.
  • #23 21605834
    jarek_lnx
    Level 43  
    Even the worst timer is no worse than 5min/month and that's 0.01%. The limitation may be the separation of the meter
  • #24 21619310
    vodiczka
    Level 43  
    chudybyk wrote:
    A small correction: the colleague did not make a wattmeter. This circuit does not measure watts...
    Don't split hairs. By the same token, you could say that a typical wattmeter does not measure watts but the voltage and current flowing through the measuring circuit and a typical laser rangefinder does not measure distance but the time it takes for the laser beam to reach its target and return to the device.
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Topic summary

A low-cost optical wattmeter concept uses a bicycle speedometer, a phototransistor (FT06-M), and a resistor (10kΩ) to measure instantaneous power and energy consumption by detecting LED pulses from an electric energy meter. The phototransistor is connected to the meter's reed switch wires after removing the battery, with the resistor polarizing the phototransistor. The bicycle meter interprets pulse frequency as speed, which is calibrated to correspond to power (watts) by adjusting the wheel circumference parameter to match the energy meter's impulse rate (e.g., 2500 imp/kWh). This setup allows the meter to display power in hundreds of watts and energy in kilowatt-hours. Limitations include the bicycle meter's quartz oscillator accuracy affecting instantaneous power measurement, but energy consumption measurement remains accurate as it counts pulses. The approach is considered a creative, indirect power measurement method rather than a true wattmeter, with some debate on its precision and practical utility compared to commercial energy meters or clamp meters. Calibration challenges arise with different impulse rates (e.g., 6400 imp/kWh) and wheel circumference settings. Alternative suggestions include using WiFi-enabled modules (e.g., ESP8266) for enhanced functionality. The method is recognized as an inventive, low-cost solution for approximate power and energy monitoring using common components.
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