0
\$\begingroup\$

I'm trying to use an LCD (DEM16101) from a uC. At some point I've connected it's power input to a 6V battery (above its 5.5 V max rating).

I can't initialize it properly so at this point I'm wondering - how can I tell if I've fried it?

\$\endgroup\$
4
  • 1
    \$\begingroup\$ Next time use a diode (1N4007) in series with your power supply to drop the voltage from 6V to aprox. 5.3V \$\endgroup\$
    – m.Alin
    Jan 3, 2013 at 16:29
  • 4
    \$\begingroup\$ @m.Alin diode voltage drop varies base on current draw. Some lcds only take 10 or 20 mA, so the diode might only drop 0.1 or 0.2v (Nokia 5510 lcd, 1n4001, in my experience). \$\endgroup\$
    – Passerby
    Jan 3, 2013 at 16:44
  • \$\begingroup\$ @passerby At 10 mA the voltage drop of a 1N4001 would be 0.6 V, according to the datasheet; but you're right in mentioning than one should take into account the current through the diode \$\endgroup\$
    – m.Alin
    Jan 3, 2013 at 23:17
  • \$\begingroup\$ @m.Alin I just checked a couple of different manufacturer datasheets, you are right. 0.6v ish at 0.01 Amps. 0.7v at 0.1A. I need to double check my last circuit then because it's not working as it should. (radioshack diodes) \$\endgroup\$
    – Passerby
    Jan 4, 2013 at 5:16

2 Answers 2

6
\$\begingroup\$

Edit: There is some argument over Maximum and Absolute Maximum values in the comments. Personally, I would still not trust the device to operate correctly, even though it has not reached or exceeded the Absolute Maximum rating. A couple comments have been made that I am incorrect in my interpretation of the datasheet. YMMV

You can tell you've fried it because you've over-volted it. I just checked the spec sheet, and 5.5V is indeed the maximum the display can tolerate. So connecting it to 6V has killed it. If you want to be really be sure you've fried, put the controller IC under an electron microscope or something and view the damage that way. Otherwise, you'll just have to assume it's gone to electronics heaven. :(

IMHO, it is a waste of time to even try to troubleshoot the display now. Even if it did work, it might stop working at any point in the future. It is no longer reliable - time to replace it! :)

\$\endgroup\$
14
  • 2
    \$\begingroup\$ datasheet page 5 show absolute max of 7 V. soselectronic.hu/a_info/resource/d/dem/dem16101syh.pdf \$\endgroup\$ Jan 3, 2013 at 16:28
  • 2
    \$\begingroup\$ No, you never know you fried it, only that it is a possibility when absolute max specs are exceeded. \$\endgroup\$ Jan 3, 2013 at 17:12
  • 2
    \$\begingroup\$ @dextorb it did not fry at 6V. 7V is the absolute maximum rating. It may not run properly at 6V, but it will not be damaged if absmax is not exceeded. That is what "Absolute Maximum" means. If it can be damaged by 6V, then what is the point of absmax spec? \$\endgroup\$
    – markrages
    Jan 3, 2013 at 19:53
  • 2
    \$\begingroup\$ @dext0rb The part may not operate within spec (or operate at all) in the 5.5->7.0V range, but it will not be destroyed. That's the difference between operating and absmax specs. \$\endgroup\$
    – markrages
    Jan 3, 2013 at 20:23
  • 3
    \$\begingroup\$ @dext0rb: Many data sheets include a note to the effect that extended exposure to near-absolute-maximum conditions may affect device reliability. I think the idea behind AMR in many cases is to provide guidance as to what sorts of protection devices are needed to protect devices from various adverse conditions. It's easier to design a device that will clamp an ESD hit to 6.9 volts without wasting power at 5 volts, than to design one that will clamp it to 5.01 volts while still not wasting power at 5.00). \$\endgroup\$
    – supercat
    Jan 3, 2013 at 21:35
7
\$\begingroup\$

You can't tell whether you fried it, that would be proving a negative. However, you should assume you fried it, especially since it doesn't appear to work anymore. You violated a absolute maximum spec, so really shouldn't be surprised. Violating such a spec is no guarantee of damage, but you can no longer rely on any other specs. Even if a over-stressed unit appears to work, it might be damaged in subtle ways and fail sometimes in some regions of its operating range.

You screwed up. Toss out the damaged device, learn the lesson, and move on. Trying to get anything useful from this device will only result in lots of frustration and probably no useful result.

\$\endgroup\$
1
  • \$\begingroup\$ Thanks for the answer. I've accepted dextorb's as he was the first one to point out the 'throw it' solution. \$\endgroup\$
    – diciu
    Jan 3, 2013 at 16:48

Not the answer you're looking for? Browse other questions tagged or ask your own question.