Bar Mode Lights Sequencer

Can drive up to 15 LEDs or LED-clusters, Selectable Bar-length

This circuit, designed on request, allows up to 15 LED clusters to illuminate in bar-mode sequence. LED sequencing will start at power-on and, after reaching the desired output, all the LEDs turn off and sequence restarts. The number of LEDs or clusters forming the bar can be selected by connecting R7 to the appropriate output pin of IC2 or IC3.

Parts:

R1,R5,R9_________1K 1/4W Resistors
R2______________33K 1/4W Resistor
R3_____________100K 1/2W Trimmer Cermet
R4_______________1M 1/4W Resistor
R6,R10__________10K 1/4W Resistors
R7,R8___________22K 1/4W Resistors
R11______________4K7 1/4W Resistor
R12_____________33R 1/4W Resistor (See Notes)
C1______________10µF 25V Electrolytic Capacitor
C2_____________100nF 63V Polyester Capacitor
C3_____________470µF 25V Electrolytic Capacitor
D1--D14________LEDs (See Notes)
Q1___________2N3819 General-purpose N-Channel FET
Q2,Q3,Q5______BC547 45V 100mA NPN Transistors
Q4____________BC337 45V 800mA NPN Transistor
IC1____________7555 or TS555CN CMos Timer IC
IC2,IC3________4094 8-stage shift-and-store bus register IC

Notes:

• R5 and D1 are optional: they could be of some utility in monitoring the sequence frequency set by means of R3.
• The terminal of R7 bearing an arrow must be connected to the desired output pin of IC2 or IC3 in order to select the number of LEDs or clusters forming the bar.
• For example: if you want to drive seven LEDs or clusters connect R7 to pin#11 of IC2 (Output 8) and the LED or cluster drivers to Outputs 1 to 7 respectively.
• Clusters can be formed by up to 12 LEDs as shown in the circuit diagram, right side. Common cluster types usually range from 5 to 10 LEDs.
• Up to 15 of these cluster driver circuits, each formed by the LEDs, two transistors and three resistors can be built and connected to the progressively numbered outputs of IC2 (the first eight clusters) and IC3 (the remaining clusters).
• If a number of clusters up to 7 is required, IC3 can be omitted.
• Constant output current value for the LEDs can be changed by varying R10.
• The formula is: R = 0.6/I (I expressed in Amperes).
• Wanting to drive only one LED per output instead of a cluster, the above mentioned cluster driver can be substituted by a single transistor, as shown in the circuit formed by D2, Q3, R8 and R9.

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Optimizing High Voltage Common Mode Circuit

Here’s a design circuit for to measure the Avago Technologies ACPL-M61L’s high-voltage common mode rejection (HVCMR). Three production samples were randomly selected for the measurements. VDD1 is the transmitter supply voltage used to turn on the LED. Limiting resistor R1 is connected to the LED anode and R2 is connected to the LED cathode. R1 and R2 connected in this common-mode fashion, rather than a single resistor, enhances CMR performance. Here’s the figure of the design circuit;

Common mode noise is often seen at the system application level where there is a diff erence in the ground levels of an isolating component’s input control circuitry and output control circuitry. This is especially true when a ground line is floating (device ground connected to a common line). In the ACPL-x6xL family, the common mode rejection (CMR) specification indicates the ability to reject common mode noise. This is also known as common mode transient rejection (CMTR). CMTR s). Thedescribes the maximum tolerable rising/falling rate of a common mode voltage (given in volts per microsecond, V/ CMTR specification includes the amplitude of the common mode voltage (VCM) that can be tolerated. The common mode voltage slew rate that the optocoupler can tolerate and hold the correct output state is referred to as common mode transient immunity (CMTI).

Common mode noise can be coupled to the opto coupler output by external circuitry. Common mode noise, especially in a high electromagnetic interference (EMI) environment, can adversely affect the output state of the opto coupler through a conductive medium, primarily capacitive and inductive parasitics, Metallic printed circuit board (PCB) tracks that operate at high frequency can couple charge to the LED input pin or to the opto coupler output pin through parasitic capacitors between adjacent metal tracks. It is often difficult to identify the root cause of common mode noise or interference that is introduced by the circuit/system/application or by other forms of external factors that couple noise. When the source of common mode noise is identified, corrective measures are easy to implement by adding decoupling capacitors or filters to the system, or by adding some form of shielding.

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