Sunday 18 November 2012

Sci Fi Siren Sound Tests


First tests of the Sci Fi Siren outlined in the previous post. The signal from the unit is a little hot so i've soldered a 68K resistor to the jack outlet from the negative to the ground to reduce it a little. I think I may up this to 200K if I take this unit out. I'm pretty pleased with the results. The LDR makes the unit quite unique, the low end bass wobbles are quite usable as well as the high squelchy sounds.

Friday 2 November 2012

Modding a Sci Fi Sound Effects Kit

My inspiration at the National Media Museum Bradford

A slight return 

 The Smartkit1035 I used in this project is available from Quasar Electronics by clicking here.


The blurb on the instruction manual states "Any science fiction fan will enjoy this space age sound effects unit. Recreate those mysterious sounds from outer space with this fun project." At less than a tenner I thought it was worth a bash. Its been a long time since I've touched electronics but my aspirations remained the same. I wanted to build a DIY siren from a cheap kit and try to document it for others to peruse.


Step 1 building the kit

The kit was very easy to build using the instructions provided. I have been playing around with breadboards and wanted to play around with the resistors to find a nice hack that would extend the range of this little kit into a usable siren. To do this I soldered jump wires in place of the resistors on the PCB, as illustrated below.


Jumper wires will be fed into a breadboard to experiment with different pots and resistors.
Note the speaker is soldered to the board during testing. 
A more detailed view of the board. Note the absence of the IC CD4001 at this stage.

Step 2 experimenting with components

Jumper wires attached to the breadboard with resistors and an LDR in place

I played around with various different components by connecting the jumper wires to the breadboard and connecting components between them. After several hours of fiddling I came up with the following components to to add to the PCB board and finish off the mod:

R1: 4.7K
R2: Light Dependant Resistor
R3: 6.8K
R4: 3.3K
R5: 100K Linear Pot
P1: 100K Linear Pot
Momentary push button - breaking the ground line from the battery clip

Breadboard with different triggers, LEDs and pots being tested.
The mighty test rig!

 Step 3 installing the remaining components

I became very friendly with my solder sucker during this stage, making sure that I did not damage the copper traces on the PCB board. If in doubt, use your iron really gently to heat the solder on the board and get the sucker nice and close. Be sure not to keep your iron on the board too long as this may damage the trace.

Completed board. Note the speaker output has been replaced by a jack input.I used electricians tape to tidy wires together and provide insulation where the jumper wires meet the wires from the battery clip
A close up of the board.

Step 4 designing the enclosure

This is the part I have struggled with in the past. I've spent some time watching Youtube videos on the subject and have invested in an HSS stepped drill bit, similar to this. I mused with the type of material I should use for my enclosure. Sure, ABS plastic cases are easy to work with, and cigar boxes from Ebay look great, but I wanted something more rugged for this unit. I settled on using a diecast aluminium enclosure (size 1590bb) from TheFuzzShack.

Once my enclosure had been delivered, I measured the interior and exterior dimensons and drew up plans of how the components would sit inside, and where the drill holes would be placed. I found it best not to rush this step, and try various different solutions to see what would fit best. Some of my sketches are included below.

Concept sketches for the case design and layout.
 Once I was satisfied with my design, I drew up a template on paper and placed it over the top of the enclosure to make sure it would fit.


Enclosure with design overlay. 





As I am going to build my siren with the screw-on plate as an access to the battery on the underside of the unit, I then trimmed down my paper template, placed it on the inside of the enclosure, and drilled pilot holes using an old upright drill I acquired last year as illustrated to the left.


I then drilled out the holes using my stepped drill bit to the required diameter for each component. The holes were easy to drill with my new bit, even the 30mm hole for the trigger button. All that remained was a little filing to remove any sharp edges.

Step 5 insulating the enclosure 

 I knew from speaking with others that the circuit my short if the metal components touched the aluminium exterior. Using my paper template again I cut out a piece of 2mm thick fibre-board and drilled holes in the correct position. I then used a glue gun to mount the LDR in place.

The paper layouts I used in this project
On testing it became obvious that the unit was still shorting. To remedy this I used the paper template again to cut out an over-sized piece of felt that would sit between the enclosure and the fibre-board. I then cut holes out of the felt for the pots and switches to poke through and held on place using magic tape.

Step 6 putting it all together and testing

Once I had everything ironed out, it was simply a case of screwing everything together and testing the unit. I took my time with this project over the space of a week, trying not to do too many steps at once and sleep on any major decisions.

I have some ideas for a case design but I'll leave that one for another post. In the mean time I need to plug this thing up to a delay line and see what I can do.... but its sounding good. I'll put some sound clips

Inside the finished unit. Note the fibre-board and felt lining.
Note the glue holding the LDR to the fibre-board
The finished unit