Could use checking of my schematic, thank you.

Thread Starter

TonyAm

Joined Oct 12, 2022
11
Hello,

I have been learning to use easyEDA to create a schematic which comprises of one Adafruit Metro Mini 328 (Arduino nano clone I think).
Also, I2C connections for an Adafruit 128x64 monochrome I2C OLED and two Adafruit MPR121 captouch boards--they share the same SDA(A4) and SCL(A5) pins.

There is also a connection for one 74HC4067 analog multilplexer breakout board similar to one sold by SparkFun. Which uses 4 digital pins of the Arduino. Audio output on pin D11, with a simple resistor/capacitor filter for output. H1, H2, H3 are just breaking out some of the Arduino's pins.

Just wondering if anyone can find any problems. Sincere thanks for any help on this.

TonyAm
Schematic_Adafruit 128x64 OLED I2c Board_2022-10-12_Crop.png
 

Jon Chandler

Joined Jun 12, 2008
433
A few minor comments:

* In general, if there are multiple ground pins (or Vcc pins) on a component or module, connect all of them. Sometimes they aren't internally connected.

* Pull-up resistors for SCL and SDA? You need one set somewhere, and not all modules will have them. I usually include resistors with solder jumpers so they can be enabled if necessary.

* Vcc and ground on H3? If you're using analog pins, you probably need one or the other if not both.
 

Thread Starter

TonyAm

Joined Oct 12, 2022
11
Thank you. The OLED and the MPR121 do have pullup resistors built in on the their boards. I did include two 1x2 connectors if you look right below the 7805 circuit. I thought if I used those extra pins (analog and digital) that I broke out into H1, H2, H3, I could use power and gnd from tapping one of the two (-)+5V connectors that I have there?
But, maybe better to include them all in one header connector (the pins and the +5V, GND)?

When you say " * In general, if there are multiple ground pins (or Vcc pins) on a component or module, connect all of them. Sometimes they aren't internally connected. " I'm not really understanding. Do You mean to connect the two (-)+5V headers together? As (-)(-)+5V+5V in a four pin header?

Thanks again,
TonyAm
 

Jon Chandler

Joined Jun 12, 2008
433
On the Arduino module, pins 19 and 20 are both grounds. I would connect both of those together. Probably not a big deal in this case, but a nice habit to get into. On some chips, the ground connections go to different parts of the chip and aren't internally connected – they have to be connected on the pcb for the chip to work.
 

eetech00

Joined Jun 8, 2013
3,418
Ok, I see. I will combine gnds on the next update. Thank you.
I don't know if your already aware of this but the ADAfruit Metro Mini already has a 5v LDO regulator (MIC5225) used on board. The output of the regulator is also brought out on the 5V pin. So you don't want to use the 5V pin as an external supply input. Use the "VIN" pin for an external supply input connection. The external supply has to be at least 6V. The 5V pin can be used as a supply source for an external circuit but you have to account for the internal current draw as well as the external current draw so the LDO is not overloaded.
 

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Thread Starter

TonyAm

Joined Oct 12, 2022
11
but you have to account for the internal current draw as well as the external current draw so the LDO is not overloaded.
Thank you. I have to figure out the external current draw. I am using an OLED breakout board (I2C), two MPR121 cap sensor touch board also from Adafruit and a 74HC4067 mux. (Thank you for those pdf files, very useful.)

Thank you for that info.
TonyAm
 

eetech00

Joined Jun 8, 2013
3,418
Thank you. I have to figure out the external current draw. I am using an OLED breakout board (I2C), two MPR121 cap sensor touch board also from Adafruit and a 74HC4067 mux.

Thank you for that info.
TonyAm
If the current exceeds the capacity of the internal LDO, you can add an external LDO. But disconnect the Adafruit 5V pin. Then use the external LDO for all external circuits. If you use a 7805, the input has to be at least 3V higher, so best to use a 9VDC supply (Wall Wort).
 

Thread Starter

TonyAm

Joined Oct 12, 2022
11
If the current exceeds the capacity of the internal LDO, you can add an external LDO. But disconnect the Adafruit 5V pin. Then use the external LDO for all external circuits. If you use a 7805, the input has to be at least 3V higher, so best to use a 9VDC supply (Wall Wort).
The "LDO" is the voltage regulator? (I wasn't familiar with that terminology, still learning).
So in this scenario, I could use an external voltage regulator (such as the 7805) to power the peripheral boards (Oled, MPR121, etc.)? (Don't use the 5V pin to supply), and then send power into which pin of the Adafruit Metro? (i.e., Vin?)

Are the two GND pins interchangeable?

Sincere thanks,
Tony
 

djsfantasi

Joined Apr 11, 2010
8,672
Assuming it is a true clone, you have two choices to power the mini:
  1. Power the mini with the 9VDC by attaching the + lead to Vin. (- connects to Gnd)
  2. Power the mini with 5VDC from the external regulator - 7805 - connecting it to the 5V pin on the mini.
The Vin pin is the input to the internal voltage regulator. Thus, connecting it to 5V won’t provide enough voltage for the regulator.

Similarly, the 5V pin is the output of the internal regulator. You can either power the mini without using Vin or power external circuits if the mini is powered via Vin.
 
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eetech00

Joined Jun 8, 2013
3,418
The "LDO" is the voltage regulator? (I wasn't familiar with that terminology, still learning).
LDO = Low Dropout (Linear) Regulator

The input voltage of an LDO can be close to, but not equal or lower than, the input voltage.
According to the datasheet, the MIC5225 dropout voltage is ~325mv, but recommends at least 1V higher than output voltage.

The 7805 is not an LDO and its dropout voltage is about 3V, so its input requires a voltage 3V higher than the output voltage.

If these input voltage requirements are not followed, the output voltage of the regulators will not be stable, and will fluctuate.

So in this scenario, I could use an external voltage regulator (such as the 7805) to power the peripheral boards (Oled, MPR121, etc.)? (Don't use the 5V pin to supply), and then send power into which pin of the Adafruit Metro? (i.e., Vin?)
Yes. That is one way to do it. See the attached diagram.
Schematic_Adafruit 128x64 OLED I2c Board_2022-10-12_Updated_Crop_mod.png

Disconnect the Adafruit "5V" pin and don't connect anything to it.
Then, connect the Adafruit "Vin" pin to the wire between the mosfet source pin and the 7805 "in" pin.
In this way, the Adafruit will get supply voltage from a 9V power supply (wall wort), and the remainder of the circuit will get 5 volts from the 7805.
Are the two GND pins interchangeable?
All ground connections should reference the same ground.
 
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Thread Starter

TonyAm

Joined Oct 12, 2022
11
Assuming it is a true clone, you have two choices to power the mini:
  1. Power the mini with the 9VDC by attaching the + lead to Vin. (- connects to Gnd)
  2. Power the mini with 5VDC from the external regulator - 7805 - connecting it to the 5V pin on the mini.
The Vin pin is the input to the internal voltage regulator. Thus, connecting it to 5V won’t provide enough voltage for the regulator.

Similarly, the 5V pin is the output of the internal regulator. You can either power the mini without using Vin or power external circuits if the mini is powered via Vin.
Thank you for clarifying these things. I understand now. Sincere thanks.
 

Irving

Joined Jan 30, 2016
3,190
The onboard regulator on the small 'Nano'-compatible boards often has minimal heatsinking so can support very few external devices before going into thermal shut down to protect itself. This can result in random, intermittent and frustratingly hard-to-identify failures and restarts. If you have an external regulated source its best to power peripherals from that and not the 5v pin.
 

Thread Starter

TonyAm

Joined Oct 12, 2022
11
The onboard regulator on the small 'Nano'-compatible boards often has minimal heatsinking so can support very few external devices before going into thermal shut down to protect itself. This can result in random, intermittent and frustratingly hard-to-identify failures and restarts. If you have an external regulated source its best to power peripherals from that and not the 5v pin.
I have had that happen in the past, it confounded me. I suspected it was some kind of power problem, but could not resolve it.
Thanks to all the help here I am learning how to apply power properly.
 

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