MQ-4 and MQ-7 as Gas Sensors

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While you may be trustworthy, "zip" files in email and malicious Web pages are a common way of introducing malware when opened (because they can be self-executing) and knowledgeable users generally will not accept them. :astonished:

Where is the crystal physically? I can the see the capacitors, which should be close to the crystal, which should be close to the device pins.

Paul__B:
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While you may be trustworthy, "zip" files in email and malicious Web pages are a common way of introducing malware when opened (because they can be self-executing) and knowledgeable users generally will not accept them. :astonished:

Oh, didn't remember, sorry

Thanks for re-posting

But there is no other way of posting the PCB files, as they come in JSON format, and this forum don't accept .JSON files

AJLElectronics:
Where is the crystal physically? I can the see the capacitors, which should be close to the crystal, which should be close to the device pins.

It is right above the MQ-7 sensor, and the two ceramic capacitors are right bellow the same sensor :smiley:

Is it bad for the circuit to be that way?

Hi,
The crystal and its two capacitors should be as close as possible to the 328.
The two caps closest to the crystal.
The LM7805 needs some bypass capacitors on its input and output, check the data sheet for values, they should also be mounted as close the LM7805 as possible.
The LM1117 also consult the data sheet for bypass capacitors.
You have the room, so make your 5v and 3.3V tracks thicker, and route your tracks wider around the component solder pads.
If you can find them, the LM555 and the 328 footprint should be available with oval/elongated solder pads rather than circular.
Like this example, it is better to solder and has a better grip of the pad to the PCB substrate.


I hope you aim to use IC sockets?

Tom.... :slight_smile:

@batista742k2

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TomGeorge:
The crystal and its two capacitors should be as close as possible to the 328.

The reasons are manyfold, EMI for one, but also to avoid the inductance of the connections pulling the crystal which can make it unreliable.

TomGeorge:
The LM7805 needs some bypass capacitors on its input and output, check the data sheet for values, they should also be mounted as close the LM7805 as possible.

.33uF input and .1uF on the output, ideally SMD, so you can get them really close to the device.

TomGeorge:
You have the room, so make your 5v and 3.3V tracks thicker, and route your tracks wider around the component solder pads.

There is merit in making all unused board area into a ground plane.

TomGeorge:
Hi,
The crystal and its two capacitors should be as close as possible to the 328.
The two caps closest to the crystal.
The LM7805 needs some bypass capacitors on its input and output, check the data sheet for values, they should also be mounted as close the LM7805 as possible.
The LM1117 also consult the data sheet for bypass capacitors.
You have the room, so make your 5v and 3.3V tracks thicker, and route your tracks wider around the component solder pads.
If you can find them, the LM555 and the 328 footprint should be available with oval/elongated solder pads rather than circular.
Like this example, it is better to solder and has a better grip of the pad to the PCB substrate.


I hope you aim to use IC sockets?

Tom.... :slight_smile:

Hi again, Tom

Thanks for the tips, I will repair the errors.

  1. What capacitors should I put in the LM7805 and 1117 terminals?
    I don't know the manufacturers of my power regulators :frowning:

  2. Why do you recommend me IC sockets?