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I am working on a project concerning the creation of a LED matrix (4 x 6) but without using a micro-controller. It will be powered by a 13V battery and the leds will be controlled by a switch. My question is about the resistors. Should I use a resistor for each led or a resistor for each line and if the latter should it be placed at the start or the end of each line ?

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  • \$\begingroup\$ get LEDs that are designed for automotive use and connect them all in parallel \$\endgroup\$ – jsotola Oct 14 '19 at 16:12
  • \$\begingroup\$ Many of the common LED strip lights have groups of three LEDs and a resistor connected in series, with many of these groups connected in parallel. \$\endgroup\$ – Peter Bennett Oct 14 '19 at 16:14
  • \$\begingroup\$ You don't give enough information for a sensible answer to be presented. What is the forward voltage of your LEDs? How many are in series to be driven by the 13V? Is the 13V a car battery (voltage up to 14V or a regulated supply? \$\endgroup\$ – Jack Creasey Oct 14 '19 at 16:25
  • \$\begingroup\$ The battery is a car battery and I want to have 4 rows of 6 LEDs each \$\endgroup\$ – Christos Xygkos Oct 14 '19 at 16:30
  • \$\begingroup\$ As per the first comment some LED modules for fancy automotive lighting come with resistors already in the modules. There are some that even allow you to cut them shorter and still run directly from a 12V source. \$\endgroup\$ – Nedd Oct 14 '19 at 16:39
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If you are controlling each LED independently then each should have its own resistor. If you are controlling a whole line/string at a time then using a single resistor per line may work out well enough.

Position does not matter as long as the resistor is in series with each LED or string. The only issue that might change this is if there is a chance you could short an LED line to ground and cause an over current condition, in that case you might want to place the resistor(s) on the + supply side.

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  • \$\begingroup\$ Basically I want all the LEDs on at the same time and I've seen designs with a single resistor either on the start or the end of the line. \$\endgroup\$ – Christos Xygkos Oct 14 '19 at 16:17
  • \$\begingroup\$ If all are always on at the same time then you may get away with one resistor for several LEDs. There will be a point where the current is difficult to control with too many LEDs in series, (the resistor needs to be lower and lower). \$\endgroup\$ – Nedd Oct 14 '19 at 16:28
  • \$\begingroup\$ And if this is used at "automotive" temperatures, it will be much harder to control. \$\endgroup\$ – rdtsc Oct 14 '19 at 18:13

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