@lotusmoon

go back to lesson electronics. You have many lack basic knowledge such as: identification of electronic components and their operation.
So follow my advice, which is not critical, I want to see my advice as a constructive one.

Here's a few PDFs with useful information for you:
http://www.rajswasthya.nic.in/RHSDP...ules/Lab Technicians/ELCTRONIC COMPONENTS.pdf
http://www.robotshop.com/PDF/eck-10-manual.pdf

 

now I am a bit confused I may have this all wrong, I had thought that the drain was connected from the LED'S and source connected to earth.

and with npn transistors i had thought that the collector connected from the LED's and the emitter connected to earth.

Yes, that's right.

An N-channel MOSFET usually replaces a NPN BJT and a P-channel MOSFET usually replaces a PNP BJT.

 

Actually, the drain is connected directed to ground, so it would be 0V. When the MOSFET is fully open, the voltage drop from source to drain is low (due to the low resistance), less than 2V (it may even be less than 0.5V).

Ooooops, I made a mistake here.

It should say:
Actually, the source is connected directed to ground, so it would be 0V. When the MOSFET is fully open, the voltage drop from drain to source is low (due to the low resistance), less than 2V (it may even be less than 0.5V).

Sorry about adding to the confusion.

 

Ooooops, I made a mistake here.

It should say:
Actually, the source is connected directed to ground, so it would be 0V. When the MOSFET is fully open, the voltage drop from drain to source is low (due to the low resistance), less than 2V (it may even be less than 0.5V).

Sorry about adding to the confusion.

Thank you for that, it makes sense now and i will proceed with a Mosfet.

 

I am looking through mosfets and they seem vastly larger voltage and amps than I am using. should I be looking for something about 15 v and 20mA or does it not matter that they are much stronger.

 

I am looking through mosfets and they seem vastly larger voltage and amps than I am using. should I be looking for something about 15 v and 20mA or does it not matter that they are much stronger.

The current will be all the current through all the diodes, which is 7*20mA or 140mA. Recently, MOSFETs are used to control motors that need several amps for starting, but you really don't need those. I would look for a MOSFET that has a current limit between 0.5A and 1A.

The voltage rating on a MOSFET tells you the maximum voltage you can use. I would look for a rating above 25V (to give you some leeway).

 

Should I be choosing N channel or p channel or does this not matter?

 

Should I be choosing N channel or p channel or does this not matter?

You would use an N-channel MOSFET for a low-side driver.

 

Thank you all for teaching me about transistors, I am now ready to build.

 

As you build, learn to doubt yourself. That means to check and recheck, and then check again the pinouts of each device. It's so very easy to turn around a transistor or misread a datasheet, or simply put the wire in the wrong hole. We've all done it, and we all try not to, but it still happens to the best of us. If you're extra careful about applying power and designing for low currents, you (your circuit) can sometimes survive a mistake.

 

Thank you all for teaching me about transistors, I am now ready to build.

This post should also help you understand.
The BJT in the common collector configuration is a high-side driver and the common emitter is a low-side driver.

Good luck.

 

As you build, learn to doubt yourself. That means to check and recheck, and then check again the pinouts of each device. It's so very easy to turn around a transistor or misread a datasheet, or simply put the wire in the wrong hole. We've all done it, and we all try not to, but it still happens to the best of us. If you're extra careful about applying power and designing for low currents, you (your circuit) can sometimes survive a mistake.

yes you were right to warn me. I have had a frustrating day.
I have been putting my 555 circuit on a pre designed 555 circuit board. But when I tested on an LED it would not flash it just stay on, when I measured the frequency it was flashing at 50 hz instead of 3 hz. I could not fix it and thought I had blown something in the 555 when soldering.
I stared again with the same result.
I tried it on my bread board with an old 555 it worked ok
I put in a new 555 the LED gave one flash and then would not work
I tried it with another new 555 the LED gave one flash and then would not work.
i put in the old 555 it worked ok but was quiet hot.
I am unsure of the value of the resister I was using and I am using 15v.
Should I be choosing a particular 555 for 15v?
I want to use 15 volts as I can put more LED's in series

 

If the 555 is getting hot, then you have too much current going through it. Do you have a resistor on the output with the LED?

 

I do have a resister on it but I think it is low resistance I will put a higher one on it. also I think I will get a holder for the 555 and solder that in so I can not damage the 555 with soldering, and also be able to swap 555's to have a better idea what is going on.
Are some 555's better able to handle high current and voltage than others?

 

Are some 555's better able to handle high current and voltage than others?

Not that I am aware of.

 

I do not know what I am doing wrong. the capacitor is 1uf the first resister is 1 r the second 260k according to my calculater this should be about 2.8 hz. but i still just get the light on all the time. I have been playing with it, resoldering, changing parts and resisters but am getting nowhere. Any suggestions?
I have copied this circuit but am using 15v. - http://www.ohmslawcalculator.com/555_astable.php

 

I'd go down to 5V until you get it working!

Did you say R1 is 1Ω? You said you copied the circuit but it seems you are using all different values, so it's hard to guess what your actual circuit is.

 

i copied the circuit but you can type in your own resistant values and it calculates the different frequencies
Tomorrow I will try 5 v.
Can the higher voltages be a problem?
thank you

 

Can the higher voltages be a problem?

An event that might be survived at 5V is fatal (for your circuit) at 15V. So, yes, 15V is a problem. It may be fine once everything is carefully arranged, but not a good place to start experimenting. Walk before you run.

 

yes I have the feel feeling I have trashed all my 555 timers.
I have been wondering if it was the high voltage causing the problem. I can run the 555 timer at 5 volt and still use 15 volts to run the LED's. I won't be able to use a moset as there will not 5 volts difference at the gate.
are mosfets better than npn transistors?
I am so thankful to this forum I had been trying for three days and about to give up as nothing seemed to be working.