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By Hunter
#199744
Hello folks!

I am in the process of making my own flashing brake light for my motorcycle.

I have a 5 volt regulator (L7805) that takes the 12v battery down for use with a 555 timer circuit. The timer circuit drives a 2N4401 transistor (NPN) that then drives a relay. For a relay I am using the "beefcake" relay kit from Sparkfun combined with two 1N4001 flyback diodes. I wasn't sure what I should connect them to so I have two diodes in there.

This in turn powers a 12V led strip which should be pulling 2.4 amps. The lights stay on, then when I hit the brake pedal it closes a switch which powers up the 555 circuit and makes them flash at around 4hz.

When I have the LED strip disconnected it works perfectly. I can hear the distinctive relay click click click and the light on the relay flashes. Upon adding a very short section of LED strip it also works flawlessly but when I connect the entire strip it flashes once or twice then just buzzes. I'm not sure what the issue is!

One other interesting thing is that when I measure the voltage going into the 5V regulator with a normal multimeter it works much better and flashes 90% of the time. What the heck!

I have the schematic below, hopefully it's readable. I'm pretty new to the world of electronics but this is stumping me! Any help would be appreciated!


Thank you!

Hunter

Image
By paulvha
#199766
I expect you have spikes on the 12V (and thus 5V) due to switching the light on/off coming from the relay contact. (NOT the coil as you have flyback diode).The 555 is sensative to spikes (having tried that in the past). I do not see the schematic, but try to work with a small capacitor on the 5V line near the 555. The fact that is works better with a normal multimeter connected could be because it acts as a capacitor to short circuit the spikes. Google on this and you will find many articles.
Paul