muckleluck

Oh wait... so you mean I should use a transistor and a power mosfet or can I drive the mosfet directly with the timer output?

sweet. thanks for the help guys.

I decided to us an astable 555 timer circuit with a 1M ohm pot and a 100 microF cap to (hopefully) give me the correct timing range. What I can't figure out is which transistor to use to switch the current to the lamp. Does anyone have any suggestions? I might need to switch up to 8A. Am I on the right track with this or is there an easier way?

I need to build a light flasher to test brake lights in cars. The input voltage is 14V and the max current about 3A. The light needs to be powered for 30s-1min (adjustable whether by a switch or a pot doesn't matter) and then off for 30s-1 min. Anybody have any suggestions for a simple circuit that can meet these specifications? Muckleluck

Ok I got it to work now on my breadboard. When I eventually put it together permanently I am going to connect a 7805 so that I have a fixed supply and a variable all in one unit. What should I use for a heat sink on the 7805 and the LM317? Muckleluck

I bought the transformer specifically for the project. It is rated 24 VA so that is more than enough for this circuit I think. The only current that I am trying to draw is whatever the 7408 requires with just the power connected.

If someone has a similar supply taht works I can only assume that I have assembled something incorrectly. I'll take a careful look at it and if all else fails start again. Thanks. Muckleluck

Hi, I don't know if someone already covered my problem in a previous reply but I too am having a problem with a power supply that I built based on the LM317. The schematic can be found at: http://www.uoguelph.ca/~antoon/circ/vps.htm My circuit is identical to this one except I haven't installed the voltmeter or the led branches. When I connect it to a 7408 TTL chip the voltage drops from 5V to 2.3V. In the construction section the author suggests adding two diodes to drop the min output voltage to zero. I found that the voltage went to 0 without them so maybe that is a problem?

With this arrangement the chip is acting like a NOR gate. If I reverse the connections so that the resistors are connected to the ground and the switches to the V+ the led will never turn off because the pins float high. Thanks for bearing with me on this line of basic questions - this is the result of a the elec education they give mech eng students. Muckleluck

Yeah it seems to be a power supply problem. I have another question about these chips. I want the inputs to be low normally and high when I press a button. How can I achieve this? Muckleluck

I'm messing around with some logic gates trying to get a basic understanding or digital logic but for some reason I can't seem to get them to work. The specific chip that I am using is a 7408 TTL AND gate. For some reason when I connect the power to the chip the voltage drops from 5 to 2.3. I can't figure out whether I have a power supply problem or I'm doing something wrong with the set up. If anyone has an idea of whats going on your help would be appreciated.