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miyek.ard
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Posted: 16 April 2018 at 12:08pm | IP Logged Quote miyek.ard

Hi peeps.

I had a Micromite Plus LCD Backpack running perfectly without any bugs or errors. Initially I powered up the board using USB console at CON8, so I fit the jumper JP1.

Then I changed the power connection from CON8 to CON1 (without removing the CON8 connection). But I forgot to remove the JP1! After some times running the MM+, the board cannot be connected to the PC anymore. It keep connect and disconnect itself from the PC. Same thing happen for any connection I made.

Is it because of the JP1? How should I address this problem?


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Azure
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Posted: 16 April 2018 at 3:21pm | IP Logged Quote Azure

First if it is not to hard I would go back to USB only power on CON8 with JP! fitted and no other power source. If that works you know your USB power and everything on the MM is OK.

Second, try powering it with JP! removed, no USB connection and power connected to CON1. If that powers up you know that the MM unit can run ok from you other power source.

Third and finally, then try and connect your USB lead again just for data (jp1 removed) and power fed to CON1 you can see if there are any problems then.

Let us know which of the three steps works or does not and what problems if any you notice. That will help us to help you if things are not working properly.
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miyek.ard
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Posted: 23 April 2018 at 1:15pm | IP Logged Quote miyek.ard

Quote:
First if it is not to hard I would go back to USB only power on CON8 with JP! fitted and no other power source.
Same problem
Quote:
Second, try powering it with JP! removed, no USB connection and power connected to CON1.
No connection at all. Tera Term unable to recognize the serial port
Quote:
Third and finally, then try and connect your USB lead again just for data (jp1 removed) and power fed to CON1
Same problem

I want to clarify that the module can be connected to the PC. Tera Term able to trace the serial port. However, when I connect the Tera Term, the connection started being unstable
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palcal
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Posted: 23 April 2018 at 3:49pm | IP Logged Quote palcal

There is a VERY stern warning in the Silicon Chip article about NOT having the jumper in place if you are using Con 1 for external power. I did read something in a thread here about it but can't remember where, but I suspect you have damaged something.
Paul.


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miyek.ard
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Posted: 23 April 2018 at 5:57pm | IP Logged Quote miyek.ard

I see. Thank you Paul! I just want to confirm regarding this matter
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robert.rozee
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Posted: 23 April 2018 at 8:34pm | IP Logged Quote robert.rozee

if you plug a mouse or keyboard into that USB port on your PC, does that mouse or keyboard work? this will tell you if you have damaged your PC's USB port.


cheers,
rob :-)
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MicroBlocks
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Posted: 23 April 2018 at 8:39pm | IP Logged Quote MicroBlocks

As shown it can happen by accident. It is the reason why i always use a 3 pin header with a single jumper.
The pin in the middle will go to the circuit and the two outer pins are either USB or other power. You then have to choose between USB and other power source.
Leave the jumper out, does not work but also no damage. Put the jumper on 1-2 or on 2-3 to select a power source. Dummy prove, but more important accident prove.
Unfortunately using diodes is not working very well as it will lower the voltage to much for most regulators. So a 3 pin jumper is the next best thing.



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Azure
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Posted: 23 April 2018 at 10:30pm | IP Logged Quote Azure

I agree with robert.rozee, you should try and connect something you know works to your PC to see if the USB port still works or is damaged.

That was what I suggested in step 1 of my post on the 16th and from your results posted today it sounds like it (your PC USB port) is not working properly anymore.

If that port does not work you should be able to try a different USB port, like one on the back of your PC.

Remember be careful and only test with either USB power only (JP1 fitted) and no external power connected OR external power only (jp1 removed). Easy mistake to make but sadly a costly one.


Edited by Azure on 23 April 2018 at 10:31pm
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panky
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Posted: 23 April 2018 at 10:30pm | IP Logged Quote panky

Aimi,

When you say "I changed the CON8 power connection to CON1", are you connecting ONLY 5V and GND to CON1?

Where you say
Quote:
Quote:
Second, try powering it with JP! removed, no USB connection and power connected to CON1.



No connection at all. Tera Term unable to recognize the serial port



- how are you connecting the Micromite to the PC in this configuration?

panky.



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twofingers
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Posted: 23 April 2018 at 11:17pm | IP Logged Quote twofingers

@MB
MicroBlocks wrote:
Unfortunately using diodes is not working very well as it will lower the voltage to much for most regulators. So a 3 pin jumper is the next best thing.

How about a Schottky diode (eg 1N5818 ) or a MOSFET as reverse polarity protection?
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MicroBlocks
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Posted: 24 April 2018 at 1:41am | IP Logged Quote MicroBlocks

@twofingers.
The problem is with USB and lots of USB cables.
The voltage under load at the end of a USB cable is often just a little above 4 volts. Worst case i had was about 3V!!! Obviously that did not work. Took me some time to figure out it was the cable.
If you add any kind of circuitry it drops alrady low voltage even lower.
The mentioned Schottky diode has a voltage drop of about 0.5 volts making the voltage that goes into the circuit (often a 3.3v regulator) as low as 3.5-3.6v. That is not enough to make the regulator work reliably. A low dropout voltage is often between 0.5-0.7v.
USB cables are often very thin cables that drop voltages significantly.
If you want a circuit to work with most USB then the only way i found was to use a jumper and select a power source.



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twofingers
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Posted: 24 April 2018 at 3:11am | IP Logged Quote twofingers

I can confirm the issues with some of the USB cables. in my experience, those with the visible shielding work best.
Just as information (I just checked it):
The voltage drop for 1N5819 for 500mA is about 0.40V, for 200mA 0.36V.
Anyway, I think it's worth trying to insert it into an existing PCB.

I like your 3 pin design! Geoff has used it for the Maximites too (AFAIK).
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