A
Allen Bong
- Jan 1, 1970
- 0
Hi Group,
My friend designed a circuit to light up an LED when a switch is
pressed. The led lighted would be duplicated to another identical
circuit board via RS232 link (2400 b/s). When an LED is lighted, the
LED would flash at 1 Hz interval. One would acknowledge by pressing
the corresponding switch on the board. Once acknowledged, the LED
would be on permanently until another switch is pressed.
The switches and LED are arranged as 2 rows of 12 . Only one switch is
allowed per row so there can only be 2 LED lighted and 2 LED in
flashing condition.
After he completed the circuit and fabricated the PCB, he wanted to add
a dimmer so he could control the brightness of all the LEDs (the
circuit is used in a boat). As you can see from the circuit below, he
turned the LED on by sourcing the LEDs and all the LEDs were common at
ground through 220 ohm resistors. So what I did is gathering all the
cathods and connected them to the drain of a MOSFET BUZ71A. This
worked fine when the brightness is high. But when the LEDs were
dimmed, the permanent lighted LED danced with the flashing LEDs and I
couldn't find a simple solution to solve it.
If instead he had sinked the current to switch on the LEDs, I would
have combined all the anodes of the LEDs and connected them to a LM317
and supplying 2V to 5V to the LEDs. But that would be major work for
him and also rewriting the PIC software.
Can someone help?
.-------------------------------------------.
| |
| PIC |
'-------------------------------------------'
VCC VCC VCC
+ + +
pulsed dc at 1Hz | | |
| |LED |LED |LED
V -> V -> V -> V ->
-LED - - -
VCC | | | |
+ | | | |
| .-. .-. .-. .-.
| | | | | | | | |
.-. | |220 | |220| |220| |220
47K| | '-' '-' '-' '-'
| | | | | |
'-' o-----------+-----+------
| |D
| ||-+
.-. 100 ||<- MOSFET
50K pot| |<---|___|--||-+
| | |S
'-' |
| ===
| GND
.-.
| | DIMMER CIRCUIT
150K | |
'-'
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
Allen Bong
My friend designed a circuit to light up an LED when a switch is
pressed. The led lighted would be duplicated to another identical
circuit board via RS232 link (2400 b/s). When an LED is lighted, the
LED would flash at 1 Hz interval. One would acknowledge by pressing
the corresponding switch on the board. Once acknowledged, the LED
would be on permanently until another switch is pressed.
The switches and LED are arranged as 2 rows of 12 . Only one switch is
allowed per row so there can only be 2 LED lighted and 2 LED in
flashing condition.
After he completed the circuit and fabricated the PCB, he wanted to add
a dimmer so he could control the brightness of all the LEDs (the
circuit is used in a boat). As you can see from the circuit below, he
turned the LED on by sourcing the LEDs and all the LEDs were common at
ground through 220 ohm resistors. So what I did is gathering all the
cathods and connected them to the drain of a MOSFET BUZ71A. This
worked fine when the brightness is high. But when the LEDs were
dimmed, the permanent lighted LED danced with the flashing LEDs and I
couldn't find a simple solution to solve it.
If instead he had sinked the current to switch on the LEDs, I would
have combined all the anodes of the LEDs and connected them to a LM317
and supplying 2V to 5V to the LEDs. But that would be major work for
him and also rewriting the PIC software.
Can someone help?
.-------------------------------------------.
| |
| PIC |
'-------------------------------------------'
VCC VCC VCC
+ + +
pulsed dc at 1Hz | | |
| |LED |LED |LED
V -> V -> V -> V ->
-LED - - -
VCC | | | |
+ | | | |
| .-. .-. .-. .-.
| | | | | | | | |
.-. | |220 | |220| |220| |220
47K| | '-' '-' '-' '-'
| | | | | |
'-' o-----------+-----+------
| |D
| ||-+
.-. 100 ||<- MOSFET
50K pot| |<---|___|--||-+
| | |S
'-' |
| ===
| GND
.-.
| | DIMMER CIRCUIT
150K | |
'-'
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
Allen Bong