tag:blogger.com,1999:blog-1523577297508817869.post3971915279148930755..comments2024-03-08T06:43:35.477-05:00Comments on Wise time with Arduino: Buy LED matrix shield kit - DISCONTINUEDFlorinChttp://www.blogger.com/profile/04330573900125042405noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-1523577297508817869.post-14364573326879735642010-10-10T13:22:04.955-04:002010-10-10T13:22:04.955-04:00You're absolutely right, but I'm talking a...You're absolutely right, but I'm talking about total 595 current, through all its pins combined. Datasheet on TI's 595 specifies 70 mA to be maximum «continuous current through VCC or GND» of 595, so in case all outputs of 595 are sourcing 20 mA this total limit may be exceeded.<br /><br />Perhaps it's not a huge problem since in most applications only a fraction of all matrix LEDs are lit so 595's don't have to source through every pin all the time.<br /><br />Nice shield anyways, kudos for sharing schematics.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1523577297508817869.post-68623805097270347882010-10-10T12:39:14.570-04:002010-10-10T12:39:14.570-04:00An output from 595 drives just one LED at any give...An output from 595 drives just one LED at any given moment. The 595 output sources a whole column indeed, but ULN2803 sinks the rows one by one, through the software. So, at any given moment, one output of 595 will only source one LED.FlorinChttps://www.blogger.com/profile/04330573900125042405noreply@blogger.comtag:blogger.com,1999:blog-1523577297508817869.post-8132905906684996622010-10-10T11:03:59.846-04:002010-10-10T11:03:59.846-04:00As I understand, ULN2803 sinks the current from fu...As I understand, ULN2803 sinks the current from full column whereas 595's drive the rows. When the whole row is lit up, doesn't 595 need to source 8×20mA = 160mA, which exceeds its maximum *total* output current?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1523577297508817869.post-89928015123052392872010-10-10T08:06:48.510-04:002010-10-10T08:06:48.510-04:00595's max output current is 25mA, enough to dr...595's max output current is 25mA, enough to drive a LED, which takes 20mA or less.<br />I have one on my desk working continuously for about a year now, and the chips are not even warm.FlorinChttps://www.blogger.com/profile/04330573900125042405noreply@blogger.comtag:blogger.com,1999:blog-1523577297508817869.post-80088764358579209482010-10-10T07:37:49.967-04:002010-10-10T07:37:49.967-04:00Why 595's are used directly without any transi...Why 595's are used directly without any transistors? They can't source enough current for the full row.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1523577297508817869.post-82869499265841107622010-06-30T12:23:58.927-04:002010-06-30T12:23:58.927-04:00I don't know what connectors you have used, bu...I don't know what connectors you have used, but those in the kit are (the only) perfect fit for the LED matrices. I built quite a few shields with great results, trust me.FlorinChttps://www.blogger.com/profile/04330573900125042405noreply@blogger.comtag:blogger.com,1999:blog-1523577297508817869.post-40388722704977666192010-06-30T11:21:05.182-04:002010-06-30T11:21:05.182-04:00Those type of female headers are pretty crappy for...Those type of female headers are pretty crappy for the thin leads of the matrices. The small pins tend to get dislodged from between the prongs of the fork shaped piece of metal inside the header.Unknownhttps://www.blogger.com/profile/06562757786888256522noreply@blogger.com