"John Fields" schreef in bericht
...
On Sat, 17 Sep 2005 15:37:10 -0500, John Fields
wrote:
On Sat, 17 Sep 2005 15:30:03 -0500, John Fields
wrote:
On Sat, 17 Sep 2005 13:56:04 -0400, "Bart"
wrote:
Hi all,
I want to make 4 LED's light up in the following sequence (looping):
O O _ _
_ O O _
_ _ O O
O _ _ O
O O _ _
_ O O _
_ _ O O
O _ _ O
the above shows it has gone through two sequences, I'll want it to be
continuous and with variable frequency (a potentiometer?)
I've read up on 555 oscillators, logic gates (nand, nor, etc.),
flip-flops,
op-amps..........
I don't know where to start. I DO have a nine volt battery and some
LEDs.
Any guidance is greatly appreciated,
Bart
---
OK, here's something that'll work using a CMOS 555 and a couple of
dual "D" type flip-flops:
---
Oops...
Forgot the ground on the power-on reset.
Also, start the thing with the pot cranked to max R. The display
should scroll at about one position change per second.
---
7555 Vcc
+-------+ |
+--|TH R|O-+
| |___ |
+-O|DIS OUT|--+
| +-------+ |
| | Vcc Vcc
+----[POT]---+ +-----+ | |
| 1M | +----|D | | [100K]
| | | | _| | |
[1µF] +------| S|O------+----+
| | | | _| | | |
| | | +--|Q R|O--+ | [0.1µF]
| | | | +-----+ | | |
| | | | HC74/2 | | GND
+-[LED]--[R]-----+ | |
| | | | | |
| | | | +-----+ | |
| | | +--|D | | |
| | | | _| | |
| +------| S|O------+
| | | | _| | |
| | | +--|Q R|O--+ |
| | | | +-----+ | |
| | | | HC74/2 | |
+-[LED]--[R]-----+ | |
| | | | | |
| | | | +-----+ | |
| | | +--|D | | |
| | | | _| | |
| +------| S|O--+ |
| | | | _| | |
| | | +--|Q R|O------+
| | | | +-----+ | |
| | | | HC74/2 | |
+-[LED]--[R]-----+ | |
| | | | | |
| | | | +-----+ | |
GND | | +--|D | | |
| | | _| | |
+-|----| S|O--+ |
| | _| |
+----|Q R|O------+
+-----+
HC74/2
The values of your LED dropping resistors will be:
Vcc - Vled
R = ------------
Iled
For your 9V supply,
Vcc - Vled 9V - 2V
R = ------------ = --------- = 350 ohms
Iled 0.02A
360 ohms is a standard 5% value, so the power they each need to
dissipate will be
(Vcc - Vled)² (9V - 2V)²
P = --------------- = ------------ ~ 0.136 watts
R 360R
so a standard 5% 360 ohm 1/4 watt carbon film resistor will be fine.
---
Crossposted to seb.
--
John Fields
Professional Circuit Designer
Looks good and a good explanation but... I'm missing a LED John. Or did you
leave it an excercise for the OP?
petrus bitbyter