This is my second entry for the 555contest.  All pictures can be clicked on to get a larger version of it.

This is a matrix of 144 small light bulbs that are flashing in a random, yet somewhat organized grouped, manner.  The inspiration for this project came from the big panels with randomly blinking lights that all large computers from the sci-fi movies back in the 60's and 70's had.

Here I'm going for a little bit of a more "artsy" style and have put all the bulbs on wires attached to the edges of a large golden picture frame.

I choose to use regular incandescent light bulbs in favor of  modern LEDs because the bulbs are more 70's, just like the 555, and also they look so much nicer with their yellow/orange glow that fades in & out instead of the harsh flashing LEDs.

All the 144 bulbs are mounted, together with its diode, in a 12-by-12 matrix where the rows are connected to Anode-drivers and the columns are connected to the Cathode drivers.

The boards handles 6 lines each so there are two Anode-, and two Cathode-boards that are put at the backside of the frame connected to the row- and column-wires.

One of the two Cathode driver boards

This is one of the two cathode driver boards. The board have six 555 ICs and six N-Channel FETs. Both are of the SOIC8 version.

As can be seen on the picture the wires that the bulbs are soldered to are just stapled to the frame and then soldered to the driver board.

Block schematic of the circuit

As can the block diagram above shows there are twelve 555s with corresponding FET drivers for the rows and the same for the columns.  The frequency of the timers are about 2 Hz with 35-40% duty cycle in order to keep the number of bulbs lit at the same time down a bit.  Since each bulb consumes 3 watt at 12 volt it would be like 450 watt of power if all bulbs are lit at the same time which is a serious amount of power. More about that later.

The low side column drivers are ok, but the anode drivers are really an ugly hack since I'm using N-channel FETs for both of them. N-channel FETs are really not suitable for the high side drivers since the Gate-Source potential have a hard time reaching a level where the FET is fully turned on.  That's why my column drivers run cold, but the row drivers gets really hot.

Schematics for 1 of 12 anode & cathode drivers

The schematic is really straightforward.  A 555 in an astable configuration modified for duty cycles less than 50%.

This is done by having the capacitor charged by the output (pin 3)  via a diode and a small resistor instead of having a the charging  resistor connected to vcc as normal.

R1 & R3= 1M and R2 & R4=300K-680K.  The R13 & R14 is on my PCBs just bridged, but it allows me to add an additional resistor in the circuit if I feel that the blinking is too fast.

The C1 & C2 capacitors are 1uF.  The FETs are FDS6680A as I already got a number of them at home.
I think I'll have to get a  dozen of P-channel FETs similar to the 6680 and redo the anode driver boards so I can leave the unit on more than a minute without fear of it failing due to heat.

Improvised analogue 12 volt power supply

If all light bulbs happen to be turned on at the same time they would require 3w*144pcs=432w = 36 Ampere!  That is quite a lot of power. No wonder that the 15 Amp power supply I first tried to use gave up as soon as I connected it.  When power is applied to the unit all 555's will be in sync and active at the same time causing a massive surge that shuts down the power supply in zero time.

In my junk boxes I found a huge old toroid transformer that have been used in an office for halogen spotlights. I don't know the power of it, but I guess somewhere between 500 and 1000VA.  After connecting a single diode  for half-wave rectifying and a 100 uF capacitor so I could measure the resulting voltage it turned out to be too high for the bag of 10 000 uF 16 volt capacitor I also found. So I had to add a tap (the black wire) to the secondary winding to reduce the output voltage of the transformer a bit.  I then paralleled 5 of the 10 000 uF capacitors and also paralleled ten 1n4001 diodes to increase the max current capacity of them to 10 Amps.

It looks like crap and most likely there's plenty of ripple when I load it with the display but it works.  Since this is a pure analogue power supply a surge doesn't bother it as much as a modern fancy switch mode PSU with oodles of protection circuitry.  It seems like I need to get a full-wave rectifier capable of handling 25 amps or so because my improvised bundle of diodes gets hot really quick. But for the time being it actually works as can be seen in the video below...  ^_^

For my second 555contest entry I need to have 144 light bulbs arranged in a neat matrix.   I tried to just solder them onto the guide/power wires by hand just approximating their positions but I quickly realized that I need some kind of a jig to hold each row of 12 bulbs in their correct positions.

After a bit of thinking I came up with an easy solution using one of my favorite building stuffs.   Hot melt adhesive (HMA) or hot glue as it's usually named.

I took a piece of metal profile as the base and then wrapped aluminum foil around the glass portion of 12 bulbs. Then I used a hefty glob of hot glue to glue the foil packages at the correct spacing onto the metal profile.

Then it was a piece of cake to solder my wire to all bulbs and getting the distance between them almost perfect.  After soldering the bulbs are easy to pop out of the jig and then put in 12 new bulbs for some more soldering.  In almost no time at all I had all 144 bulbs soldered on to their respective wires.

Tomorrow I'll hopefully get my frame so I can mount all wires onto it.

The BippetyBoop is my first entry in the 555contest.  (Video at the bottom of this post)

It's a random tone generator sounds a little bit like the sound effects that 60's and 70's move producers liked to have when a large computer with a a lot of flashing lights was computing something.  The timbre of the sound is not right since it's just a plain square wave, but the pitch and speed is not too bad :)

BippetyBoop block diagram

The circuit consists of four 555 timers, one 324 quad opamp  and one 4016 bilateral analogue switch.

The block diagram at the right shows the basic function of the circuit.

The first 555 is used to generate triangular/ramp waveform. Instead of using the regular output at pin 3 I take the signal from pin 2 connected to the timing capacitor charging up and down during the cycle.

In order not to affect the charging of the capacitor  this voltage need to be buffered by one of the opamps in the 324 set in a regular voltage follower configuration before it can be used by the rest of the circuit.

This voltage is used to control the pitch of the output.

The second 555 is a needle pulse generator I.E. a square wave with a very low duty cycle.  The pulses are like a few milliseconds long and repeated at about 2 Hz.  These pulses determine the speed of the beeps - so here I got about 2 beeps per seconds.

The output of the needle pulse generator is connected to two things.  First it's controlling one of the switches in the 4016 that allows the buffered voltage from the ramp generator to reach the holding capacitor during those few milliseconds when the pulse is high.  When the pulse goes back to low the switch is opened and capacitor is isolated from the varying voltage and is keeping the value for a while.

Since the needle pulses are not synchronized with the ramp generator this means that the holding capacitor will have different random voltages changing two times a second.

To actually use this signal without affecting it a second voltage follower from the 324 is connected to the holding capacitor.

The other thing the needle pulse generator is doing is to trigger the third 555 that is configured as monostable timer. For each short pulse from the needle pulse generator the monostable will output a pulse that is about 300 mS long

The fourth 555 is the just a standard square wave oscillator at a frequency about 1KHz.  The CV (Control Voltage) input of it  is connected to the buffered holding capacitor so the frequency will change according to the voltage at the capacitor. The Reset input is connected to the output of the monostable so it will only produce sound during the 300 mS the monostable is active for each pulse.

All in all this will produce short random beeps at a rate of about two beeps per second.

BippetyBoop Schematic - Click for full size

IC1-4: NE555  IC5: HC4016  IC6: LM324  C1,C5,C6: 100nF C2,C3,C4,C7: 1uF
R1,R2: 22k  R3: 470k  R4: 2.2k  R5: 100k, R6,R7: 10k  R8: 1k  D1: 1N4148

I first prototyped this on a breadboard using standard PTH components, then I etched a pcb for SMD components.  Unfortunately I didn't have any SMD diodes at home, but a standard 1N4148 is small enough to be mounted as a SMD part quite easily.  What was worse is that I discovered that I only had the 4016  in TSSOP version instead of the SOIC that I made the pcb for. I didn't feel like making another pcb so I just patched it in with a few old wirewrap wires and then put a glob of hotglue on top of it for stability.

The breadboard prototype and the SMD version

And finally after all this jibba jabba - the video!