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Topic: MKR1400 GSM 5V problem when using VIN (Read 254 times) previous topic - next topic

MarkSolcom

I thought I'd share this since it had me scratching my head for a while.

I have a simple project that interprets a signal received on a radio receiver module, displays the results on an OLED display then uploads them via GSM.

Everything works fine if  I use the USB input to power the system but powering via Vin results in unpredictable and erratic behaviour of the receiver and OLED. Attaching or omitting the battery makes no difference.

It turns out that there is a design flaw in the MKR1400 which, unlike other Arduinos, does not have a voltage regulator on the VIN circuit. According to the specs VIN must be 5V.

On the MKR1400 (and probably other MKR boards as well) VIN connects via a Schottky diode (Q2B) which has a forward voltage drop of about 1V which means that the 5V bus becomes more like 4V which was the cause of my problems.

The solution for me was simply to bridge the 5V and VIN pins which are adjacent anyway.

A quick glance at the schematics doesn't suggest any issue with this, providing I don't plug in the USB at the same time but I would appreciate a peer review of the solution and possibly a comment from teh designer.

smgs

Also interested in this. hopefully sandeepmistry comes along shortly and can answer this one.

Cheers

a_guadalupi

Hi, yes there is the diode in between so it drops a bit (around 300mV) the solution of making a jumper can be used or you can simply connect your display directly to the 5V VIN source. This is better since the 5V on the board is limited in current by a PTC, so if you need more than 500mA in total this can cause the PTC to interrupt the current flow

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