Questions about a reed sensor circuit?
Hi Electronics Experts,
I'm looking at possibly buying this reed sensor from eBay.
As you can see, the title is "Reed sensor module magnetron module reed switch MagSwitch For Arduino NEW SN"
And the not very helpful description is:
Questions:
Q1. Where the description says "refrigerator", is it likely to be talking about a fridge door alarm?
Q2. If so, what else would I need, to get this working as a fridge door alarm (on the outside of the fridge)? Just a magnet, battery and piezo buzzer?
Q3. Can this be used to have no battery drain while the fridge door is closed?
Q4. What is the likely output voltage?
Q5. What is that blue component which seems to have a rotary adjustment, and what is its purpose?
Q6. What does "Working distance: 1.5 M" mean? Distance from what?
Q7. Is that chip likely to be a 555 timer, which allows time before producing output?
Q8. What are those 3 legs sticking out the end likely to be for? I assume this is output, but why 3 rather than 2?
Q9. Is it likely to be similar in function to this more expensive item from a local electronics shop?
Q10. Why does this more expensive one have 4 legs?
Please number your answers accordingly for clarity.
Thanks.
I'm looking at possibly buying this reed sensor from eBay.
As you can see, the title is "Reed sensor module magnetron module reed switch MagSwitch For Arduino NEW SN"
And the not very helpful description is:
Features:
Sensor Module
Apply to switchboard, duplicator, washing machine, refrigerator, camera, disinfector, electronic scale, juice level gauge, gas meter and water meter, etc
Specifications:
With fixed bolt hole for easy installation
Working distance: 1.5 M
Operating voltage: 3.3 V-5 V
Output Type: Digital switching output (0 and 1)
Size: 3.2 x 1.9 x 0.7 cm
Net weight:4 g
Package weight:14 g
Color:As shown in the pictures
Package Content:
1 x Sensor Module
Sensor Module
Apply to switchboard, duplicator, washing machine, refrigerator, camera, disinfector, electronic scale, juice level gauge, gas meter and water meter, etc
Specifications:
With fixed bolt hole for easy installation
Working distance: 1.5 M
Operating voltage: 3.3 V-5 V
Output Type: Digital switching output (0 and 1)
Size: 3.2 x 1.9 x 0.7 cm
Net weight:4 g
Package weight:14 g
Color:As shown in the pictures
Package Content:
1 x Sensor Module
Questions:
Q1. Where the description says "refrigerator", is it likely to be talking about a fridge door alarm?
Q2. If so, what else would I need, to get this working as a fridge door alarm (on the outside of the fridge)? Just a magnet, battery and piezo buzzer?
Q3. Can this be used to have no battery drain while the fridge door is closed?
Q4. What is the likely output voltage?
Q5. What is that blue component which seems to have a rotary adjustment, and what is its purpose?
Q6. What does "Working distance: 1.5 M" mean? Distance from what?
Q7. Is that chip likely to be a 555 timer, which allows time before producing output?
Q8. What are those 3 legs sticking out the end likely to be for? I assume this is output, but why 3 rather than 2?
Q9. Is it likely to be similar in function to this more expensive item from a local electronics shop?
Q10. Why does this more expensive one have 4 legs?
Please number your answers accordingly for clarity.
Thanks.
ASKER CERTIFIED SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
I am not German, at least not yet. I only live in Germany. 100 EE point will do the job : ).
Indeed, probably I was writing as you changed the original Q3. It took me a while to type in…
A3a. No.
Or at least not so simple.
The idea is that you need the reed switch board powered all the time, so it is active when you open the door and will provide the signal for Arduino.
What you could do, in order to save energy from battery, is to think that a mini/micro Arduino board will go in “SLEEP” mode when consumes almost no energy at all, even if it is powered. Then you have maybe next option.
You use only reed switch or Hall sensor attached to Arduino, so no more your original reed switch board. And when the switch is activated, then it produces a external interrupt to Arduino which will wake up from sleep very fast and start the buzzer. Then when the door is closed and the buzzer is shut off, then goes in sleep again and consumes almost no power from battery.
But one more thing, is not written in specs, but you should measure the current drawn by the reed switch board when the reed switch is not triggered and you maybe will be surprised that is very low if you disconnect that LED from board which indicated power. LM393 may draw under 1mA, typical 0.4mA, so almost nothing.
A11. If you look at the picture of the board and follow the PCB tracks you may see that “+” and “-” are in fact in parallel with the reed switch. I only can suppose that those additional holes are for another type of sensor instead of reed switch, maybe one which requires + and -, so the same breakout board is used/sold with other sensors too. It has nothing to do with the battery. Or maybe if you do not want to use the LM393 signals, then you just solder 2 wires at that reed switch there and use it directly to Arduino.
A12. They call it sensitivity in advertising of selling pictures. Of course the reed switch will have the fixed around 1.5cm sensitivity distance when will close. You cannot change how the reed switch close with that potentiometer. The potentiometer is used to set up a triggering level for LM393 which acts as comparator, because you have a range for VCC 3.3-5V, so you may need to play with the potentiometer depending by your VCC voltage applied and see how the reed switch closes versus output from LM393. It is nothing complicated, juts paly with it and you will understand in 5s.
If you have a piezo buzzer which sounds continuously when a battery is connected, then of course you do not need an oscillator, a microcontroller to make the sound. You just need a contact or a digital output to apply the voltage from battery when the switch is triggered.
Now, the delay problem, is your old 555 timer problem.
Then you buy a small Arduino if you do not want 555 timer. You need a timer somehow.
Arduino is better a nice to work with.
As we agree 100EE points, but to be fair we count all your questions, not to mention A3 is double, so we have Q3a with answer A3a, because of the changes, the last questions are not marked with Q13 and Q14, so you owe me around 15x 100EE : ))) = 1500 points, not bad for this morning…
Indeed, probably I was writing as you changed the original Q3. It took me a while to type in…
A3a. No.
Or at least not so simple.
The idea is that you need the reed switch board powered all the time, so it is active when you open the door and will provide the signal for Arduino.
What you could do, in order to save energy from battery, is to think that a mini/micro Arduino board will go in “SLEEP” mode when consumes almost no energy at all, even if it is powered. Then you have maybe next option.
You use only reed switch or Hall sensor attached to Arduino, so no more your original reed switch board. And when the switch is activated, then it produces a external interrupt to Arduino which will wake up from sleep very fast and start the buzzer. Then when the door is closed and the buzzer is shut off, then goes in sleep again and consumes almost no power from battery.
But one more thing, is not written in specs, but you should measure the current drawn by the reed switch board when the reed switch is not triggered and you maybe will be surprised that is very low if you disconnect that LED from board which indicated power. LM393 may draw under 1mA, typical 0.4mA, so almost nothing.
A11. If you look at the picture of the board and follow the PCB tracks you may see that “+” and “-” are in fact in parallel with the reed switch. I only can suppose that those additional holes are for another type of sensor instead of reed switch, maybe one which requires + and -, so the same breakout board is used/sold with other sensors too. It has nothing to do with the battery. Or maybe if you do not want to use the LM393 signals, then you just solder 2 wires at that reed switch there and use it directly to Arduino.
A12. They call it sensitivity in advertising of selling pictures. Of course the reed switch will have the fixed around 1.5cm sensitivity distance when will close. You cannot change how the reed switch close with that potentiometer. The potentiometer is used to set up a triggering level for LM393 which acts as comparator, because you have a range for VCC 3.3-5V, so you may need to play with the potentiometer depending by your VCC voltage applied and see how the reed switch closes versus output from LM393. It is nothing complicated, juts paly with it and you will understand in 5s.
If you have a piezo buzzer which sounds continuously when a battery is connected, then of course you do not need an oscillator, a microcontroller to make the sound. You just need a contact or a digital output to apply the voltage from battery when the switch is triggered.
Now, the delay problem, is your old 555 timer problem.
Then you buy a small Arduino if you do not want 555 timer. You need a timer somehow.
Arduino is better a nice to work with.
As we agree 100EE points, but to be fair we count all your questions, not to mention A3 is double, so we have Q3a with answer A3a, because of the changes, the last questions are not marked with Q13 and Q14, so you owe me around 15x 100EE : ))) = 1500 points, not bad for this morning…
ASKER
Thanks again, Viki.
Q13. Can you provide a link to an appropriate (and cheap) Arduino, in case I do ever want to explore that option?
Q14. Since the eBay sensor module has no ability to delay the output (e.g. 60 secs after fridge door is opened), it seems to me that for the purposes of making a fridge alarm, this module is not significantly better than having a reed switch connected to a battery connected to the buzzer which connects back to the other leg of the reed switch (i.e. just 3 items connected in series with wire). Correct?
Q15. Is it correct to say that a switch which opens only when a magnetic field is near, is referred to as "Normally Closed" (NC)?
Q16. What are the cheap options for such a switch (e.g. are there reed switches which are NC, or hall sensors, or what)?
Q17. What is your nationality then, Viki? I'm from NZ.
Q13. Can you provide a link to an appropriate (and cheap) Arduino, in case I do ever want to explore that option?
Q14. Since the eBay sensor module has no ability to delay the output (e.g. 60 secs after fridge door is opened), it seems to me that for the purposes of making a fridge alarm, this module is not significantly better than having a reed switch connected to a battery connected to the buzzer which connects back to the other leg of the reed switch (i.e. just 3 items connected in series with wire). Correct?
Q15. Is it correct to say that a switch which opens only when a magnetic field is near, is referred to as "Normally Closed" (NC)?
Q16. What are the cheap options for such a switch (e.g. are there reed switches which are NC, or hall sensors, or what)?
Q17. What is your nationality then, Viki? I'm from NZ.
A17. For the rest I will answer you later. I am RO.
ASKER
Thanks Viki.
As far as I know, you're the first RO I've spoken to.
As far as I know, you're the first RO I've spoken to.
ASKER
Hi again Viki,
Re Q16. Here's one workaround for this problem:
http://www.instructables.com/id/Make-a-Magnetic-Reed-Switch-Work-Backwards-sort-o/
https://www.youtube.com/watch?v=Bagu71qkUiM
but I'm still keen to hear your answer to Q15.
TRS
Re Q16. Here's one workaround for this problem:
http://www.instructables.com/id/Make-a-Magnetic-Reed-Switch-Work-Backwards-sort-o/
https://www.youtube.com/watch?v=Bagu71qkUiM
but I'm still keen to hear your answer to Q15.
TRS
A13. I searched some online stores on NZ and Arduino is expensive there.
For your application Arduino Nano will be enough.
http://www.hobbyist.co.nz/?q=arduino-nano
http://www.surplustronics.co.nz/products/7233-arduino-nano-v30-atmega328-
http://www.surplustronics.co.nz/products/7190-pro-mini-module-atmega328-5v-16m-for-arduino
http://nz.element14.com/arduino/a000005/atmega328-arduino-nano-eval-board/dp/1848691
http://www.mindkits.co.nz/store/p/7014-Funduino-Nano-Low-Cost-100-Clone.aspx?status=1
https://nicegear.co.nz/electronics-gear/dfrduino-nano-v31/
Look, on ebay US from China:
http://www.ebay.com/itm/CH340G-USB-Nano-V3-0-ATmega328P-5V-16M-Micro-Controller-Board-Arduino-Cable-/171982902871?hash=item280afad657:g:NQwAAOSwT5tWMepM
or direct from China:
http://www.aliexpress.com/item/Nano-V3-ATmega168-CH340-MicroUSB-Compatible-for-Arduino-Nano-V3/32572993712.html?spm=2114.30010308.3.1.bbbBQQ&ws_ab_test=searchweb201556_0,searchweb201602_4_10017_10005_10006_10034_10021_507_10022_10009_10020_10008_10018_10019,searchweb201603_6&btsid=3b920f99-4319-4081-b5c2-5f66113ac92a
For your application Arduino Nano will be enough.
http://www.hobbyist.co.nz/?q=arduino-nano
http://www.surplustronics.co.nz/products/7233-arduino-nano-v30-atmega328-
http://www.surplustronics.co.nz/products/7190-pro-mini-module-atmega328-5v-16m-for-arduino
http://nz.element14.com/arduino/a000005/atmega328-arduino-nano-eval-board/dp/1848691
http://www.mindkits.co.nz/store/p/7014-Funduino-Nano-Low-Cost-100-Clone.aspx?status=1
https://nicegear.co.nz/electronics-gear/dfrduino-nano-v31/
Look, on ebay US from China:
http://www.ebay.com/itm/CH340G-USB-Nano-V3-0-ATmega328P-5V-16M-Micro-Controller-Board-Arduino-Cable-/171982902871?hash=item280afad657:g:NQwAAOSwT5tWMepM
or direct from China:
http://www.aliexpress.com/item/Nano-V3-ATmega168-CH340-MicroUSB-Compatible-for-Arduino-Nano-V3/32572993712.html?spm=2114.30010308.3.1.bbbBQQ&ws_ab_test=searchweb201556_0,searchweb201602_4_10017_10005_10006_10034_10021_507_10022_10009_10020_10008_10018_10019,searchweb201603_6&btsid=3b920f99-4319-4081-b5c2-5f66113ac92a
A14: YES.
A15: YES.
A16:
http://www.ebay.com.au/itm/NC-NO-Optional-Door-Window-Contact-Magnetic-Reed-Switch-Alarm-Security-10-20mm-/300960282044?hash=item4612a175bc:g:ga4AAOxy7f5SMkHv
http://www.aliexpress.com/af/NC%252F-NO-Optional-Door-Window-Contact-Magnetic-Reed.html?ltype=wholesale&d=y&origin=n&isViewCP=y&catId=0&initiative_id=SB_20160423010736&SearchText=NC%2F+NO+Optional+Door+Window+Contact+Magnetic+Reed
The advantage of Arduino is that you can change digital in the program NO with NC.
Of course you may do that also with a transistor and some resistors.
A15: YES.
A16:
http://www.ebay.com.au/itm/NC-NO-Optional-Door-Window-Contact-Magnetic-Reed-Switch-Alarm-Security-10-20mm-/300960282044?hash=item4612a175bc:g:ga4AAOxy7f5SMkHv
http://www.aliexpress.com/af/NC%252F-NO-Optional-Door-Window-Contact-Magnetic-Reed.html?ltype=wholesale&d=y&origin=n&isViewCP=y&catId=0&initiative_id=SB_20160423010736&SearchText=NC%2F+NO+Optional+Door+Window+Contact+Magnetic+Reed
The advantage of Arduino is that you can change digital in the program NO with NC.
Of course you may do that also with a transistor and some resistors.
ASKER
Thanks very much for all your excellent answers, Viki!
I'll get back to you if I have any more questions. If appropriate I might open another question.
I'll get back to you if I have any more questions. If appropriate I might open another question.
I will post here below few more ideas if they come into my mind.
For example the 1-10min timer with 555 instead arduino:
http://www.electroschematics.com/5963/adjustable-timer-1-10-minute/
I know you would need something like that:
https://www.itead.cc/12v-delay-timer-switch-module-adjustable-0-to-10-seconds.html
http://wiki.iteadstudio.com/12V_DELAY_TIMER_SWITCH_MODULE_ADJUSTABLE_0_TO_10_SECONDS
only that you need 3V or 4.5V on batteries.
That ca be achieved easy with any microcontrooler.
Below is the transistor+resistor that I was speaking before, in case is not enough current from microcontroller for the buzzer, in the link you replace the relay coil with the buzzer.
http://electronics.stackexchange.com/questions/220492/safely-pull-5v-to-gnd-on-3-3v-gpio/220504
Below are some ready-made timers which may suit to your application:
http://www.aliexpress.com/item/DC-3V-30V-DIP-Timer-Control-Switch-Module-Relay-LED-Timing-Controller-6V-12V-24V-free/32423347935.html
http://www.aliexpress.com/store/product/DC-3V-30V-DIP-Timer-Control-Switch-Module-Relay-LED-Timing-Controller-6V-12V-24V-free/1881254_32423347935.html
http://www.ebay.com/itm/171559563058
http://www.ebay.de/itm/like/281828819820?lpid=106&chn=ps&ul_noapp=true
http://www.ebay.com/itm/DC-3V-30V-DIP-Timer-Control-Switch-Module-Relay-LED-Timing-Controller-6V-12V-24V-/171559563058
http://www.ebay.com/itm/DC-3V-12V-Delay-Timing-Timer-Module-Max-4-Minutes-Adjustable-With-Trigger-Button-/131643890947
For example the 1-10min timer with 555 instead arduino:
http://www.electroschematics.com/5963/adjustable-timer-1-10-minute/
I know you would need something like that:
https://www.itead.cc/12v-delay-timer-switch-module-adjustable-0-to-10-seconds.html
http://wiki.iteadstudio.com/12V_DELAY_TIMER_SWITCH_MODULE_ADJUSTABLE_0_TO_10_SECONDS
only that you need 3V or 4.5V on batteries.
That ca be achieved easy with any microcontrooler.
Below is the transistor+resistor that I was speaking before, in case is not enough current from microcontroller for the buzzer, in the link you replace the relay coil with the buzzer.
http://electronics.stackexchange.com/questions/220492/safely-pull-5v-to-gnd-on-3-3v-gpio/220504
Below are some ready-made timers which may suit to your application:
http://www.aliexpress.com/item/DC-3V-30V-DIP-Timer-Control-Switch-Module-Relay-LED-Timing-Controller-6V-12V-24V-free/32423347935.html
http://www.aliexpress.com/store/product/DC-3V-30V-DIP-Timer-Control-Switch-Module-Relay-LED-Timing-Controller-6V-12V-24V-free/1881254_32423347935.html
http://www.ebay.com/itm/171559563058
http://www.ebay.de/itm/like/281828819820?lpid=106&chn=ps&ul_noapp=true
http://www.ebay.com/itm/DC-3V-30V-DIP-Timer-Control-Switch-Module-Relay-LED-Timing-Controller-6V-12V-24V-/171559563058
http://www.ebay.com/itm/DC-3V-12V-Delay-Timing-Timer-Module-Max-4-Minutes-Adjustable-With-Trigger-Button-/131643890947
Here are further ideas implemented by others:
http://www.instructables.com/id/Fridge-Door-Detector-Alarm/
https://www.eeweb.com/blog/extreme_circuits/fridge-door-open-alarm-circuit-project
http://electronicdesign.com/analog/alarm-sounds-when-refrigerator-door-remains-open-too-long
http://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/files/29/20806/fig_01.gif
http://adaptivepath.org/ideas/adaptive-path-fridge-alarm/
Or ready-made, next only measuring the temperature, without any magnetic switch:
http://www.ebay.com/itm/Acu-Rite-Wireless-Refrigerator-Freezer-Thermometer-with-Alarm-00986A2-/381602642017
http://www.ebay.com/itm/Wireless-Digital-Thermometer-Refrigerator-Freezer-Temperature-Alarm-Programmable-/262120372985
Or ready-made as you want:
http://www.alibaba.com/product-detail/Small-Magnetic-Sensor-Refrigerator-Door-Alarm_60337009869.html?spm=a2700.7724857.29.10.17VDIA&s=p
http://www.alibaba.com/product-detail/10mm-Precision-90dB-AA-2-Wireless_1252711721.html?spm=a2700.7724857.29.121.17VDIA
http://www.alibaba.com/product-detail/refrigerator-door-alarm-H0T129-window-door_60391821685.html?spm=a2700.7724857.29.112.17VDIA
http://www.alibaba.com/product-detail/refrigerator-door-alarm-door-alarm-sensor_1975104756.html?spm=a2700.7724857.29.175.17VDIA
http://www.ebay.com/itm/Visit-Guests-Wireless-Security-Systems-Alarm-Notification-Window-Front-Door-Open-/181872499475
http://www.ebay.com/itm/2x-Magnetic-Reed-Switch-Normally-Open-or-Closed-NC-NO-Door-Alarm-Window-Security-/172090495434
http://www.ebay.com/itm/Magnetic-Wireless-Home-Window-Door-Open-Entry-Alarm-Sensor-System-Anti-Burglar-/231445111032
http://www.instructables.com/id/Fridge-Door-Detector-Alarm/
https://www.eeweb.com/blog/extreme_circuits/fridge-door-open-alarm-circuit-project
http://electronicdesign.com/analog/alarm-sounds-when-refrigerator-door-remains-open-too-long
http://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/files/29/20806/fig_01.gif
http://adaptivepath.org/ideas/adaptive-path-fridge-alarm/
Or ready-made, next only measuring the temperature, without any magnetic switch:
http://www.ebay.com/itm/Acu-Rite-Wireless-Refrigerator-Freezer-Thermometer-with-Alarm-00986A2-/381602642017
http://www.ebay.com/itm/Wireless-Digital-Thermometer-Refrigerator-Freezer-Temperature-Alarm-Programmable-/262120372985
Or ready-made as you want:
http://www.alibaba.com/product-detail/Small-Magnetic-Sensor-Refrigerator-Door-Alarm_60337009869.html?spm=a2700.7724857.29.10.17VDIA&s=p
http://www.alibaba.com/product-detail/10mm-Precision-90dB-AA-2-Wireless_1252711721.html?spm=a2700.7724857.29.121.17VDIA
http://www.alibaba.com/product-detail/refrigerator-door-alarm-H0T129-window-door_60391821685.html?spm=a2700.7724857.29.112.17VDIA
http://www.alibaba.com/product-detail/refrigerator-door-alarm-door-alarm-sensor_1975104756.html?spm=a2700.7724857.29.175.17VDIA
http://www.ebay.com/itm/Visit-Guests-Wireless-Security-Systems-Alarm-Notification-Window-Front-Door-Open-/181872499475
http://www.ebay.com/itm/2x-Magnetic-Reed-Switch-Normally-Open-or-Closed-NC-NO-Door-Alarm-Window-Security-/172090495434
http://www.ebay.com/itm/Magnetic-Wireless-Home-Window-Door-Open-Entry-Alarm-Sensor-System-Anti-Burglar-/231445111032
ASKER
Thanks again, Viki!
ASKER
Amazing answer, thank you! You Germans are thorough! I hope it's OK if I pay you your $100 in local currency (i.e. EE points).
Unfortunately, I edited my original post after opening it, so it looks as if you haven't seen this inserted question:
> "Q3. Can this be used to have no battery drain while the fridge door is closed?"
And here's some follow-up questions:
Q11. If the battery would be connected to 2 of the 3 pins, what are the "+" and "-" holes at the other end of the board for?
> "The potentiometer is used to adjust the trigger level, in other words works as kind of “sensitivity” adjuster."
Q12. Sensitivity to what? Distance from the magnet? If so, how is this possible? I thought the reed switch would have a fixed amount of sensitivity to magnetism.
> "You need a magnet to activate the reed switch. Then you need a battery (what voltage we discuss later) for the power. You need a buzzer for the sound, alarm."
Good, those are the 3 things I suggested Q2.
I have a piezo buzzer which sounds continuously when a battery is connected, so I guess that means I don't need the micro-controller, right?
But what is going to cause the delay (say 60 secs after the fridge door is opened) before the buzzer sounds?
Thanks again.