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Old 7th Apr 2020, 2:33 pm   #1
Ken
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Default Zener diode problem with Banggood kit.

I suspect like many here just now I'm in lock down and in my case I'm not even supposed to leave the house. I have built Banggood kits before and apart from the lack of any instruction etc they have generally been OK and good value for money. This one is called an IR Detector and I bought it some time ago. Here's a link to Banggood's information on it which for these kits is quite good and includes a circuit diagram.
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https://m.banggood.com/DIY-IR-Infrared-Sensor-Switch-Kits-Infrared-Proximity-Switch-Circuit-Board-Electronic-Training-Kits-p-1300901.html?rmmds=newArrivals#popupStatedetail
The kit contains 3 LEDs (one IR transmit, one IR receiver and an ordinary red LED). There are 5 diodes. Two of these are 1N4007 and the other 3 are said to be zener diodes. This is where my problem lies as one of these is missing from the kit. They are shown on the circuit diagram as 4148 though the symbol for a zener diode is not used. The diodes themselves are marked st4148. I can only find a reference to a 1N4148 on the net. This is not a zener diode. I downloaded a data sheet for these which gives the package size which seems to be the same as the 4148s in the kit though I realise this probably doesn't mean much. I have some 1N4148s. I also have some zeners i.e. BZX85 3.6V, BZX85 5.6V (not sure why these have the same number but different voltages), BZX61 7.5V and BZX79 9.1V. I I'm hoping the some one more knowledgeable than me could have a look at this and perhaps suggest a replacement for the missing diode from the ones I have. I've attached the circuit diagram for convenience.

Regards,

Ken.
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Old 7th Apr 2020, 3:13 pm   #2
jimmc101
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Default Re: Zener diode problem with Banggood kit.

The 1N4148 is a small signal silicon diode and is the correct part for D6, 7 & 8. The zener diode reference must be a mistake.

Section C of the HEF4093 forms a relaxation oscillator, without D6 and R11 the mark:space ratio would be approximately 1:1, D6 and R11 modify this to approximately 5:1 so that the LED is only on for 20% of the time.

D7, R4 and R13 are a puzzle they appear to be a crude attempt to offset the threshold of section D of the '4093, why I don't know.

D8 allows C3, R5 & VR1 to set the ON time once triggered, it stops C3 discharging back into the 4093.

To repeat use your 1N4148s the are correct for this circuit.

Jim
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Old 7th Apr 2020, 3:13 pm   #3
Ambientnoise
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Default Re: Zener diode problem with Banggood kit.

Circuit wise, they don’t look like zeners, just small signal diodes such as 1N4148. I would just use a 4148 from your stash.

Another Ken
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Old 7th Apr 2020, 3:22 pm   #4
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Default Re: Zener diode problem with Banggood kit.

Hi Jim and "Another" Ken,
Thank you both for your replies and telling me what I needed to know.

Regards,

Ken.
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Old 8th Apr 2020, 7:04 pm   #5
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Default Re: Zener diode problem with Banggood kit.

Just an update on this. Kit is now built and working.

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Ken.
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Old 9th Apr 2020, 10:41 am   #6
Ambientnoise
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Default Re: Zener diode problem with Banggood kit.

Good work, thanks for letting us know. Just what does it do exactly, the link is not very informative.

Ken
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Old 9th Apr 2020, 6:30 pm   #7
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Default Re: Zener diode problem with Banggood kit.

It has an IR tx and rx. They are mounted along side each other. When it's powered if you move your hand above these it operates a small relay and operates the red LED mounted beside it on the same board. I've tried it with my hand about 2ft above and it seems quite sensitive. The sensitivity can be adjusted. I think it would work at a greater distance though don't know how reliable it would be. According to the markings on the relay it would switch 230V at 3A though I don't fancy trying that. The idea reminds me a bit of the break beam alarms you could make with an old black painted OCxx transistor with the paint removed. Not very useful but I bought it as one of Banggood's "flash deals" so it was very cheap. I was just looking for something to do when I built it so I don't really have a use for it. Thanks again for the help.

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Ken.
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Old 11th Apr 2020, 8:49 am   #8
Ambientnoise
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Default Re: Zener diode problem with Banggood kit.

Thanks, those kits sound like they can be excellent value.
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Old 11th Apr 2020, 10:13 am   #9
Ken
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Default Re: Zener diode problem with Banggood kit.

The only drawback is if you use the free post option they take up to five weeks to come. I'm not usually in a hurry so it's not an issue for me.

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Ken.
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