New Design Questions

End Devices (Nodes)
1

Hi.

I’m new to the community but I’m keen to be part of this and learn about the technology. I made a design for a board in Eagle. Trying to bypass power demands of the arduino pro mini and avoid overhead I don’t need.

I would love it if anyone experienced in circuit design could cast their eye over the schematic and give me any comments. I have made a few circuitboards with the ESP8266 in the past and I typically leave out something OBVIOUS.

As I say that it occurs to me that having my own voltage regulator on board kind of kills the power saving thing. Not sure how to overcome that. Power the ATMEGA and RFM95 direct off the battery without regulation?

LoRaUltrasonic

2

@mundenez
Welcome on board, to be able to help you, the main question is how you need/want to power your board?
Avoid regulator is fine but need descent battery approx 3V to 3.6V
Why do you need 5V and a level shifter on 2 I/O?

3

I use the NCV8170 series LDO (usually 3V3) for most of my low power projects because the Iq is only 500 nA. On-board regulation is strongly recommended.

1 Like
4

It’s a 5V ultrasonic sensor. I have had some success changing the 5v signal down with a voltage divider and the 3.3v signal is ok to trigger … normally… I’ve had spurious results and in my discussions with an electronic engineer he said the correct way of doing it is with a level shifter.

I will be powering the board with a Lithium Ion battery so voltage is ~3.x to 4.2V - Hence some sort of regulation is required I guess. - I know that some regulators do need a significant step up to function ie 3.3v in = 0v out 4.2vin = 3.3v out

5

The NCV8170 input voltage range is 2.2 - 5.5 V.

6

I took your advice. I found that NCV8170 but man does it have a tiny package : Capture.
I’m not used to working with such tiny footprints.

7

Also available in XDFN-4 foot print 1,mm/side with corner pads - even smaller! :wink:

8

You have the board space, so perhaps provide an easy to solder alternative ?

The MCP1700 has an IQ of 1.6uA typical, and goes up to 250mA output. Available in a range of packages, including a T092 through hole type.

And if your using a LiPo it is prudent to add the option for an on-board polyfuse, remember LiPos can put out a lot of current.

9

Its not difficult to modify an Arduino Pro Mini for low current operation.

If you replace the regulator with a low current LDO type, such as the Torex XC6204 (IQ of 100nA!) and remove some resistors you transform the Pro Mini into a low current wonder. It can be cheaper to do this than buying and fitting the separate components.

10

TPS78233 is also 500nA IQ and max out 150mA but it’s SOT23 package easy to solder :wink:

http://www.ti.com/lit/ds/symlink/tps782.pdf I’ve ordered some sample last week.

11

I might switch to a bigger package. I’ll be getting it made for me but I’d prefer the 250mA option. My current draw is max 110mA as I see it but better safe than sorry.

Thanks for the advice re the fuse. I’ll do that.

Does anyone know what DIO1,2 and 5 do on the RFM95? I was copying a schematic but I’m not sure it’s needed?