TCS decoders. Do LEDs require resistors?

[craigolio1]

Hello all. I'm installing a TCS K0D8C in a Kato N Scale F40ph. The diagram shows the LEDs connected directly to the function outputs. Do these decoders not require a current limiting resistor?

Thanks.

Craig

[peteski]

Does the manual mention anything specific about it (either way)?  Does the manual also mention hooking up either 12V or 1.5V light bulbs to the same pads? Or are those strictly LED outputs?

[jagged ben]

The manual appears to show separate return connections for LEDs for the first four functions, suggesting that those pads have resistors.    Compare to the last two functions which go back to the regular blue common and say 12V.    Also the photo clearly shows 1000ohm resistors connected in series to each of the 'LED+' pads.   So NO, you do not need to add resistors as long as you use these pads.

Kind of weak documentation, if you ask me, (although better than Digitrax, which has none!), but I'm near certain you can do it.  It really boggles my mind a bit that decoder manufacturers go to the extra effort of designing these features and then do nothing to call attention to them.   

Also kind of weird that they put the resistors on the common side, so that you can't just still have all returns going to common.   Digitrax does it the other way (when they do it). 

[peteski]

Individual resistors on the common positive does seem unusual. But that leaves open the possibility of using devices other than LEDs with those functions, then connecting their other sides to common positive (blue).  However if I wanted to run remote wires to a front headlight and 2 ditch lights, using the built-in resistors I would end up with 6 wires. If I did the same circuit using resistors on the function output side I would only need 4 wires. I also don't like for the manufacturers to pick the resistor value for me. I like to use m own resistors to determine the brightness of the LED.  But that's me . . .

[mu26aeh]

From TCS page,

"Drop-in decoder for Kato N Scale engine: F40PH. 8 Function with Auto Adjusting Back EMF and built-in onboard resistor for an LED . 2 Onboard superbright, Golden White LED's, with short leads. 1 Amp motor drive 2 Amp peak. Note: Four of the functions (F1-F4) have onboard resistors for LEDS and 1.5v bulbs. The remaining two hardwire functions (F5-F6) output at 12v and will need external resistors if you plan to use LED's or 1.5v bulbs.

This decoder features onboard 680 ohm 1/4 watt resistors for LED's!"

[craigolio1]

Thanks guys. I completely missed the fact that the four function outputs say LED and have separate returns, and the others share a common return and say 12v.

I like to use resistors to control brightness as well so I'll likely add another in series.

Craig

[jagged ben]

Individual resistors on the common positive does seem unusual. But that leaves open the possibility of using devices other than LEDs with those functions, then connecting their other sides to common positive (blue).  However if I wanted to run remote wires to a front headlight and 2 ditch lights, using the built-in resistors I would end up with 6 wires. If I did the same circuit using resistors on the function output side I would only need 4 wires. I also don't like for the manufacturers to pick the resistor value for me. I like to use m own resistors to determine the brightness of the LED.  But that's me . . .

Yeah I agree with all that.   Plus TCS put 1k ohm resistors on there which is pretty high.  Digitrax uses 470ohm, iirc, which is about the minimum needed to protect most LEDs from overcurrent.  That means you get a fairly maximally bright headlight and you can put another resistor in series if you want to make it dimmer, which makes more sense if you ask me.  If TCS 1k ohm brightness is too dim for you can't make it brighter without re-wiring everything to different pads.  I suppose in either case if you're not happy with the factory resistor you can choose your own value and install to the other pads like on decoders without that feature, but still... 

[Wutter]

You can also adjust the brightness of each output using the CVs, I would suggest trying that out as well and seeing if you can get settings you want.

https://www.tcsdcc.com/Customer_Content/Technical_Info/Tech_Manuals/Comprehensive%20Programming%20Guide.pdf

[craigolio1]

Thank you.