Discrete Chain Link Oscillator
Introduction: Discrete Chain Link Oscillator
The following project will describe how to turn 5 discrete components into a building block which when serially connected will form an extendable flashing lighting chain.
Just a simple discrete solution without the aid of a microcontroller. Even so each block can have a different coloured LED and these can be assembled within the chain in any colour combination required.
Not a replacement for a Neopixel just different.
Supplies
Point LED red*
BC849 SOT23*
*equivalent components may be substituted.
47K 1206
470R 1206
10uF/16V Electrolytic
21 AWG solid core Enamelled copper wire or flexible wire.
Eagle PCB software
FlatCAM
Candle GRBL
3018Pro or similar
Single sided copper clad PCB board
Alternative Assembly - Stripboard
NPN Transistor (ZTX337)*
3mm Low Current LED*
*equivalent components may be substituted.
47K resistor
470R resistor
10uF/16V Electrolytic capacitor
One set of components per block is required. Just multiply the component (5) by the number of blocks.
Stripboard.
I have no affiliation to any of the suppliers you may have your own preference, the links are only provided for reference and more detail.
Step 1: Basics
The circuit is based on a transistor configured as a fixed bias, common emitter mode switch.
In this configuration RB is connect to the +V supply and the base, we need the base emitter voltage (VBE) >0.7 for the transistor to be switched on and VCE will be <200mV
With the junction of RB and the base connected to 0V then VBE=0V and the transistor is turned off VCE=+V. 134
Therefore with a switch connected from the junction of RB and base to 0V we can switch the transistor on and off.
With the switch open we have a current path via RB with a transistor being a current amplifier we need sufficient current at the base to fully switch the transistor on but how do we know what is sufficient current.
If we connect an LED to the output in addition to a resistor we can see when the transistor switches on.
Using a 5V supply the LED which has a forward voltage VF of ~1.6V and the difference between this and the supply is 4.3V. Imax=V/R therefore if 5mA is through the LED then RLED=860R
Assuming a gain of 100 for the transistor it could be more of less, for the existing components If its significantly less than Imax will be lower and may not light the LED but if it is greater than we will not get more than Imax as its limited by the components and the supply.
Therefore, IB = IC/Gain = 50uA and RB = (5-0.7)/IB = 86kR
With these values and a switch we can turn the LED on and off.
However, this is a manual operation and we want the LED to switch on and off automatically for as long as required.
If we consider a serial Resistor/Capacitor network with a 5V supply and the switch in parallel with the capacitor.
Apply the power and the capacitor will charge up via the resistor until is equals ~5V. this charging will take some time which is calculated by RC, if we take R=86kR and C=10uF the time (Time constant), will be 0.86 seconds.
In reality the capacitor is only charged to 63% of 5V in this time and over the next 37% charges more slowly and to all intents and purposes takes 5 time constants to fully change or 4.3 seconds.
Returning back to the switch if we now close it this discharges the capacitor in RC seconds but as the switch is effectively 0R then time = 0 seconds. In the circuit transistors replace the switches.
Now we have switching control for the LED and a timing element we have our basic building block.
On its own nothing will happen but if connected to a duplicate building block with feedback we have the classic Multi-vibrator.
Step 2: Multi-vibrator
Why is the building block half a multi-vibrator when we can just build a full multi-vibrator.
In the classic configuration we have a closed loop that appears tied together but if we reconfigure this circuit you can see that its 2 identical sub blocks and we simply connect them together in a chain of sub blocks serially with a single feedback path
In connecting the 2 halves of the Multi-vibrator together how do they then work. 71