Power supply issues?

Other Hardware General Electronics
1

Hello,

I'm using an 'MB102 Breadboard Power Supply Module' to power temperature measuring circuits and getting some erratic readings.

First off I did the Arduino tutorial project with temp/humididity sensor and lcd display which worked fine. Then I changed to a thermistor circuit with lcd which also worked fine when powered by the programming cable but when I switched to the MB102 the temp reading started jumping up and down by several degrees.

Both circuits use a nano with its 5V/gnd pins connected to breadboard rails powered by the MB102 and a wall wart.

So what could cause the bad readings? Why would only the thermistor circuit be affected? Why is it then fine when powered through the nano's USB port?
So many questions :slight_smile:

Thanks for any help
Yarbles.

2

I have a feeling your wall wart is 5V out, and feeding into the barrel jack will not give you 5 volts out you are expecting. As anything changes on the load the 5V voltage will change causing your reference to change and give you unstable readings. If I am correct changing the wall wart to maybe 8-12V will solve your problem. I do not have your schematic so this is a first order guess.

3

It's a 9V supply and I just found the MB102 is bad, putting out 9V thru the 5V pins. Should have measured that sooner ::).

So now I have a 5v power supply plugged directly into the nano and measurements are good but now all the power for the 16x2 LCD is coming from the nano 5V pin. Is that OK long term or should I use a new MB102 or something else?

4

The LCD requires very little current you will be ok stealing power from the nano.

However if your LCD has a backlight it should be OK but it would be good to know the backlight current.

5

Unfortunately, the "MB102 Breadboard Power Supply Module" is at least as useless as the on-board regulator on the Nano and for the same reason. The regulator on both has almost no heatsinking and will overheat and - hopefully reversibly - shut down with any substantial current draw.

For any serious project, use a 5 V regulated supply such as a USB "phone charger". You can pass up to 500 mA through the USB port though on a Nano, you lose the voltage drop of the series diode to the "5V" terminal and the actual ATmega328 chip.

The "MB102 Breadboard Power Supply Module" can be fed with 5 V through its USB connector though on most, this is a female connector and requires a male-male "A" cable.