Trying to build flashing unit using a 555 chip.
Directions call for .01 MFD, disk capacitor. The old unit which no longer works had a disk capacitor, about 3/16 in. in diameter, with 103M printed on it. I used one from Radio Shack that is 1/4 in diameter , and reads 104M.
It doesn't work. As soon as 9 vdc is applied both lights come on to about a 6 volt intensity and then alternate flashing on up to 9 volt intensity.
First question is, how does 103M correlate to .01MFD?
Second, is the difference between 103 and the 104 significant enough to be causing the bulbs to stay partially illuminated?
103M means 10x10^3 pf, or 10000 pf, which is .01mf
104M means 10x10^4 pf, or 100000 pf which is .1mf, 10 times too big.
The number 3, or 4, or 5 is how may zeros to add on at the end, the first 2 digits are the value. The M is 20% tolerance.
http://stason.org/TULARC/pc/how_to_read_capacitor_codes.html
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Capacitors are rarely, if ever, rated in millifarads (mfd, note the lower case "m" which is the abbreviation for "milli" or times .001. An upper case "M" is "Mega" which is times 1,000,000, a big difference). It is more likely microfarads, the normal abbreviation is the greek letter "mu" which resembles a lower case "u" with an extra tail on the front. Micro means times .000001
M is definitely tolerance, not an abbreviation for milli, micro, or mega. See the link I posted.
I thought caps were more often rated in nanofarads
For a simple flasher with a one second flash rate find your self an LM3909 flasher IC and about a 220uF electrolytic capacitor. This circuit will run for about one year on a triple A cell.
The LM3909 is discontinued but they are still available. For instance I have 25 of them in my parts box.
rrinker M is definitely tolerance, not an abbreviation for milli, micro, or mega. See the link I posted. --Randy
On the first part, I was refering to your first and second lines where you translate picofarads into millifarads. Although the conversion is correct if you meant microfarads, the use of millifarads is very uncommon. I went on to point out a common error in posting the upper and lower case "M" which shouldn't be confused and why it shouldn't. Also note the original poster stated "a .01 MFD disk capacitor" which prompted this.
JSperan I thought caps were more often rated in nanofarads For a simple flasher with a one second flash rate find your self an LM3909 flasher IC and about a 220uF electrolytic capacitor. This circuit will run for about one year on a triple A cell. The LM3909 is discontinued but they are still available. For instance I have 25 of them in my parts box.
A nanofarad capacitor is getting pretty small. "Nano" is half way between "pico" and "micro." For some reason,over the years, capacitors skipped over "milli" and "nano" prefixes. The reason predates my involvement in electronics.
After finding out the LM3909's were discontinued, I was glad I had a small stash of them. They're the easiest way to make an LED flasher circuit. Several of my cars have self contained operational FRED's based on this IC. I've found that shelf life of the power cell is more an issue than the power draw of the circuit.
TomDiehlAfter finding out the LM3909's were discontinued, I was glad I had a small stash of them. They're the easiest way to make an LED flasher circuit. Several of my cars have self contained operational FRED's based on this IC. I've found that shelf life of the power cell is more an issue than the power draw of the circuit.
Yes, nice chip, too bad they couldn't sell enough of them to hobbyists to keep it in production.
The chip is still available from one of my suppliers at a not too unreasonable cost. They also appear on eBay at a rather inflated price.
I agree, shelf life is likely a greater concern than power consumption.
The funny thing about the 3909 is - you can take a big giant 40 pin 8-bit CPU (the RCA 1802 - think 3909's are hard to find, try finding one of those) and hard wire the address and data pins to make an LED flasher that draws a fraction of the power of the 3909 circuit. It's just a tad bit larger....
One of the small PICs might actually be lower power than a 3909, of course the downside is you need to write a program to make the LED flash on and off, and get it loaded into the PIC. But this is pretty much why 3909's have disappeared.