New to Arduino need a little help

Hi, my name is Dan, I am no stranger to electronics, been in the field for over 50 years, I am new however to the Arduino. I have only had one for less than a month now and am excited to learn how to make it do the things I want. That being said, I need to know if this layout will work or if not what should I do to fix it.
I have 3 man doors that I want to monitor. Each door will have a fingerprint scanner for entry. I have a 12 V power supply with battery backup to provide all the power to the system. Door open monitoring and Exit request to exit through the door.
Not sure if the serial line of the Arduino can have more than one device on at a time is why I thought using the 8:1 Serial expander would be the right choice.
I am showing the 8:1 serial expander and fingerprint scanners as perf-boards because the parts are not in the data base of Fritzing, which I used to do the layout.
With your EXPERT knowledge I should have this layout corrected real quick… then start working on the code to make it work. Thanks

Could Your system act like the Arduino checks the doors for access requests? That loop will surely be fast enough. In such a way the demands for hardware will be a lot lower.

Image from Original Post so we don't have to download it. See this Simple Image Guide

...R

Fritzing images look nice but they generally don't convey much information. In the case of your diagram it is impossible to read the pin labels. A photo of a hand-drawn circuit diagram would be much more informative.

I'm not sure what your question is.

If you want advice about the serial expander please provide a link to its datasheet.

...R
Serial Input Basics - simple reliable ways to receive data.
Several Things at a Time

Hi Dan, welcome to the forum.

I am no stranger to electronics

Please give us more detail about your level and area of experience, because what you posted so far indicates to us a low level of experience.

Also please read the forum guide in the sticky post. Every new forum member should read this before their first post. But many do not and you are one of them. We can tell that just from the title you gave your post.

As mentioned, your Fritzing diagram is very poor, but I spotted several errors already.

  • Your buttons are wired incorrectly, causing floating inputs. They should be connected to ground and INPUT_PULLUP used.
  • Your power supply, 12V 3W, looks inadequate for relays and solenoids. What will the maximum current draw be? We need clickable links to all components please.
  • There is no common ground between the Arduino and power supply
  • There is a black object connected to the barrel input of the Uno. A linear regulator? The Barrell input can take 12V, but the Uno won't be able to power other devices with 12V input because the regulator will overheat. I suggest a 12V to 5V DC-DC convertor to power the Uno, though it's 5V pin, and other devices.
  • The multiplexer idea won't work because the Uno won't know which input to listen to. It may be possible to avoid using the multiplexer by using one of the more advanced software serial libraries, which uses pin change interrupts.

Paul

Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

A hand drawn circuit with pin labels and component labels will be more informative as we are in troublshooting, not design mode.
A hand drawn circuit has infinite component symbols to choose from.

What are the motor control modules?

Thanks.. Tom... :slight_smile:

If your expander is this:-

Then I don't think it will work for you. It is a bit naughty of them to advertise this device as a serial port expander when what it actually does is to switch one of 8 pairs of signal to one pair of outputs.

It will only work if you can switch to a channel and talk to a serial device. If you have more than one serial device sending a signal at the same time then you will miss the signal you are not switched to.

In your case there is no control over when a fingerprint scanner will send you data, it just sends it when it is ready. Therefore it can't be used for what you want.

A true serial expander would have a built in FIFO buffer for each channel so that things are not missed when the Arduino is not looking at that particular channel. You are best getting a Mega which has three extra serial ports and can handle what you want directly.

Grumpy_Mike:
In your case there is no control over when a fingerprint scanner will send you data, it just sends it when it is ready.

I missed that earlier.

I agree that a Mega is the practical solution.

...R

I thought of that too:

PaulRB:
The multiplexer idea won't work because the Uno won't know which input to listen to. It may be possible to avoid using the multiplexer by using one of the more advanced software serial libraries, which uses pin change interrupts.

But checking the software serial libraries, I don't think any of them will listen on 3 ports simultaneously. At the moment, Mega is the only simple solution I can think of.

Some of the Teensy boards also have multiple serial ports. Check out:-Teensy Technical Specs Comparision Table

There is away to cheat with ‘some’ serial devices..

Transmit may be wired to several receivers - as long as they don’t overload the pin, but all devices will ‘get’ the same transmitted data at the same speed...

Received data may be diode-OR’ed together (schottky)... as long as you can ensure the idle data states are the same - and - that only one sender device is talk ng at a time... and you can identify which device that is.

[[ I’ve used this (in the old days) with multiple RS232 modems on a single serial pair - but these devices only ‘talked back’ when they were ‘asked’ to, so there were no collisions in the received data.
This was done for a very specific reason, as there was only one available pair for hundreds of kilometres... ]]

If you’re local and have the option, there’s no substitute for multiple hardware serial ports.

Looking back at the OP, I can't see any need for a single Arduino to control all 3 doors. Why not have one Arduino per door? Then the need for multiple serial ports goes away. A Nano/Pro Mini/Pro Micro per door should be ok, each connected to it's fingerprint reader, button, relay, solenoid etc.

Thanks to all of you for responding. I have a degree in drafting… got it long before CAD. I also have a degree in Electronics… studied tubes. Worked for the last 20 years installing, servicing, programming, and testing… fire alarm systems, sound systems, nurse call systems, access control systems, security systems, and clock systems. AS you see the word “system” is part of everything I worked with… that is why I was using only one Arduino. I came to the same understanding as PaulRB just the other day… 3 Arduinos will work fine… I have been looking at the Nano. All I need to know is after taking the 12 volt supply through a regulator down to 5 volts… what is the pin out for the micro usb… not sure… been looking online… nothing really yet.
Again all of you have been great in giving me help and understanding about this new project of mine…
Oh I am 73 years only and retired… do need some help now and then… Thanks to you all.

DanRecord:
All I need to know is after taking the 12 volt supply through a regulator down to 5 volts… what is the pin out for the micro usb…

Not sure what you are asking there… the two things don’t immediately seem related! Also, the Nano has mini-USB, not micro-USB.

What I am concerned about is this. The Nano can be powered by 12V (Vin pin) but at such a high voltage, it can’t really power anything else that requires significant current at 5V. 3.3V, even less so. Those fingerprint scanners contain powerful CPUs and will pull a lot of current, which could overload the Nano’s regulator. So I would recommend a 12V-5V DC-DC converter. This can power the Nano (via 5V pin) and the scanner.