Power/failsafe LED

[talulah]

Thats useful for people, Bob. Note that 10mA is normally easily sufficient for an LED. You do not need to use the current in the datasheet that the forward voltage drop is specified at - less is enough normally.

Generally the datasheet will have a graph of voltage and current. For example, the LED here: http://homepages.which.net/~paul.hills/Temporary/Hewlett%20Packard%20HLMPK105.pdfhttp://homepages.which.net/~paul.hil...%20HLMPK105.pd f on page 3. The graph at the top left of page 4 shows the luminous intensity linear with current, but the human eye is sort of logarithmic, so halvingthe intensity doesnt make the LED appear half as bright.

Off topic this, but amazingly the retina cells in the human eye can actually detect just one photon!

[stu]

Oh right. cool.

Mr Stu

[turps]

is it not a good idea to mount a small peace of metal on to the removable link that could fit into fuse holder and then have the fuse holder next to the other half of the removable link on the robot then with a standard 9v battery power an led it would still go out when the link was removed and wouldnt go out just because there was a fault with the speedos in my mind it would be a lot simpler and possably more relyable would this be allowed

[jim]

thats just trying to emulate the behaviour of a properly wired power led and acts as a get-around for the rules which is meant to be there for safety reasons and the led could go out if the 9v battery went flat and the robot could still be powered and a little punctuation in your posts wouldnt hurt nor would the odd capital letter

[turps]

in all fairness jim i cant pic fault with anything youve said however i have no idea how to make the led come on without having it on a separate power supply because i have no idea where to put it on my speed controler if anyone knows where to place the power light on the 4qd ncc 70 i would be more than happy to do it but im not going to risk blowing up one of the most expensive peaces of kit in my robot for a rule that has more holes in it that a string vest and the reason i dont use puncuation as a mater of principal if we did without it before the 1500s we can do without it now

[blazerbotics]

why do you have to connect it across the 4Qds? none of our power lights are connected across the speedos. We just use a 24v LED from RS, which can connect anywhere in the circuit.

[jim]

Connect it between the main battery positive and negative leads after theyve passed through the link (with an appropriate resistor if necessary.) This is electrically equivalent to connecting it between the battery terminals on the speed controllers. Thats assuming you have a normal electrical setup.

[ewan]

I thought Id do a quick sketch to help you out with the wiring (see the picture on my profile) the Robot LED unit can be just a little panel-mount LED that you can get from Maplin, that will run at 24v (I used to make LED units, but I hadnt done the research and after Id started making mine I found maplin mass produce them which made them cheaper than the ones I sold :sad anyway, I hope that helps.

[geoff]

This is the final wording to be placed in the rules regarding failsafe lights. As agreed by the committee at last Saturdays meeting.

4.3
In addition to the main power light (See. Batteries and Power no. 6.8.) showing the main power is activated. An additional light may be fitted to indicate the robot is in a fail-safe mode. This will be at the discretion of the robot constructor. Even if such a light / indictor is fitted, the robot constructor will still be required to demonstrate that the robot is able to fail-safe under power. ref rule 4.2

Geoff Smith.
Chairman, Fighting Robot Association.