Checking cabling of ItsyBitsy M4; simple beginners request

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HansH
 
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Checking cabling of ItsyBitsy M4; simple beginners request

Post by HansH »

I include a sketch of the wiring, I tried.
I would be happy, if some experienced user might check it for mistakes, I made.
Central is an Adafruit ItsyBitsy M4 Express featuring ATSAMD51

General:
I want to measure temperatures, using a PT1000 sensor
the measured temperatures should be transmitted through RS232
External power is DC 24V
I want it programmed in Circuit Python.

Within the sketch I noted the names of allused parts

I would be happy to receive some comments.
  • Is the Capacity required to avoid initial voltage peaks on switching power on?
  • How could I avoid destruction of the StepDown Unit on wrong polarity connecting the 24V ?
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dastels
 
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Re: Checking cabling of ItsyBitsy M4; simple beginners request

Post by dastels »

Looks reasonable at a glance.

The capacitor is to smooth out any glitches on the 24v line since digital electronics like a nice clean power source. It will also remove and poweron spikes providing a smooth increase in voltage when power is applied.

To polarity protect it, the simplest is to use a keyed connector that can't be connected wrong. For electronic protection, have a look at the circuit in the top left of the motor shield schematic: https://learn.adafruit.com/assets/9536. It's typical of the driver boards that take an external power source.

Dave

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HansH
 
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Re: Checking cabling of ItsyBitsy M4; simple beginners request

Post by HansH »

@dastels Thank You for looking onto my sketch.

Some consecutive questions:

Regarding protection of the StepDown against wrong polarity:
Was a diode, parallel to the capacity and the StepDown, a reasonable idea, shortcutting the external power in case of wrong polarity?

Was the capacity probably required for protection or is the fact, that the StepDown is dimensioned for up to DC50V and should be connected to only DC24V sufficient against the turn-on voltage peak ?

General:
To build this setup in a final permanent, mechanically robust arrangement, insensitive to vibrations, what was a suggested base? Is a soldering bread board suitable, using pin-headers so mount and contact and using jumper wires solded with the soldering bread board?
Or was it more stable, using the mounting holes and M3 hex-spacer to mount it on some other plastic board and connecting between the ports directly with soldered jumper wires?

I include a scetch, showing an image of a virtual arrangement on a soldering breadboard.
Image
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dastels
 
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Re: Checking cabling of ItsyBitsy M4; simple beginners request

Post by dastels »

A diode in parallel would cause a short circuit. It might protect your circuit but something on the 24v side might burst into flames.

Voltage is irrelevant, powering on could produce a spike. The capacitor also smooths the voltage as I mentioned.

Mounting the ItsyBitsy, soldering all it's pins on the ItsyBitsy and the board it's mounting on will suffice for it, but the other boards only have pins on one side so there is the danger of them "flapping" if there is vibration. If vibration is that much of a concern I would use their mounting holes to secure them to the board in addition to the header pins being soldered.

Dave

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HansH
 
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Re: Checking cabling of ItsyBitsy M4; simple beginners request

Post by HansH »

@dastels

Regarding wrong polarity protection:
A diode in parallel would cause a short circuit. It might protect your circuit but something on the 24v side might burst into flames.
That will inform the person, connecting in wrong polarity, that he made a mistake :-). But yes, there might be a better solution :-)
  • What about connecting a diode in line with the StepDown, blocking the wrong polarity?
Regarding switch-on spike protection:
Voltage is irrelevant, powering on could produce a spike. The capacitor also smooths the voltage as I mentioned.
The description of the StepDown (Pololu) emphasizes, that about double voltage is important for selecting the protection capacitor against the power-on spike. https://www.pololu.com/product/2843
  • What about putting a Transient Voltage Suppressor (TVS) diode parallel to the StepDown, instead of the capacity? Was the TVS oder the capacitor a better choice for this pupose ?
This post now got a more electronic character. Should I move a copy to the other part of the forum?

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Re: Checking cabling of ItsyBitsy M4; simple beginners request

Post by dastels »

It's important to use a capacitor, it does more that handle the initial spike. The higher voltage rating is so the spike doesn't blow it out.

A diode in series might do the job.

Dave

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HansH
 
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Re: Checking cabling of ItsyBitsy M4; simple beginners request

Post by HansH »

@dastels

Thank's a lot

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