Well, if you answered yes to any of the previous questions, I would like satisfy that urge for all you hackers, tinkerers and explorers out there. I'd like to dive a bit deeper into the world of Sifteo where things could get scary for some. Need not worry though, I will try my best to guide you though the process of hacking the brains of our current design so you can use your stereo or headphones instead of the built in speaker.
But why didn't you guys build a headphone jack into the system from the get go?!
Good question! We definitely thought about this during our engineering process. What led us to not include it in the final design was the fact that we believe that Sifteo is a social platform. We want to encourage our customers to interact not only with the system but the people around them as well.
So why write this article? Aren't you encouraging me to be a hermit?
One of the main use cases where we have seen the need for a headphone jack is for loud environments. If you're playing a game like Bleep, F.R.E.S.H or Low Rollr at a party you might want bigger sound. Something the little amplifier in our base that it just can't handle. You can also, if you chose, plug in your headphones as well.
Who the heck are you?
Another fine question. I'm Jared one of the hardware engineers from Sifteo. As a member of a small team, I helped develop the system from its infancy all the way to the point of mass production. It's been exciting to develop a new game platform and even more exciting to share a little bit with everyone how it came to be!
What' s next?
Take a look at the checklist section to make sure this is a good project for you. It should also give you an idea of the journey that awaits you. Also, feel free to read the full blog post I wrote on tech.sifteo.com to get a little more information about this hack but also about the other inner workings of everything that is Sifteo.
Step 1: Checklists Checklists Checklists
1. You have the courage to brave new worlds.
2. You have had some hands on soldering experience. (the more the better)
3. You have the proper tools. (see the list below)
4. You have had some hands on practice with all the other tools listed (especially drill).
So, lets get started!
I do have to warn you that you will be modifying the plastics of the Sifteo Base. This will involve some cutting and also some drilling. and will void the warranty. If you would like to keep everything pristine then this tutorial is not for you.
0. Eye protection - Safety glasses are a must. I generally always use my microscope but when I don't I opt for eye safety glasses.
1. Sifteo Base
2. Stereo audio jack (Digikey Part Number: CP1-3524NG-ND )
3. 26 AWG Solder Spool (or similar)
4. Soldering iron - anything with a good tip should suffice. We use the Weller WD-1M in the office.
5. Pair of wire strippers - the generic yellow ones are great
6. Pair of flat edge cutters - can't leave home without them
7. Extra 26 AWG Wire (Digikey Part Number: A3049B-100-ND) -- make sure what ever wire you use is stranded -- not solid core
8. A single stepper bit or drill bits in these sizes: 1/16", 1/8",3/16"
9: Hot glue/hot glue gun -- I prefer this over superglue. (especially when I make mistakes!) It can be easily heated up for removal.
Not required but recommended:
1. Hakko FA-430 - we use this guy to suck away all the harmful soldering fumes. I don't do soldering anymore without some type of exhaust fan.
2. CSI 825A Hot Air Station - obviously not everyone is going to have a hot air station sitting around but if you do take advantage of it! You can also use a hair drier or the like. More details on its use later on. (i'm also a fan of the first(?) generation of Weller's 6966C. The new versions don't seem to get as hot though)
Step 2: Lets talk circuits!
Our current design, instead of using an IC (integrated circuit or chip), uses a discreet circuit made of passive components and an H-Bridge. H-Bridges are useful in many ways besides actuating motors back and forth. They can also be used for audio!
The illustration of this configuration known as a Bridge Tied Load (BTL). Besides being composed of an H-Bridge (two half bridges) it also consists of an analog low pass filter composed up of 3 capacitors and 2 inductors.
First, lets look at the circuit.
Take a gander at circuit diagram provided. This was actually one of the circuit diagrams used to prototype this circuit before it made its way onto the Base PCB. The main advantage of this circuitry is that it can be used to deliver a signal to the speaker that is 2x the rail voltage. Or, in other words, we can get bigger sound out of a smaller power supply voltage. This is a common technique that most (if not all) class D ICs use to generate sound for your iPhone speakers and even home theater. The purpose of the filter is to remove all the harsh "edges" from the sound which are created from the square PWM waves. Typically you want your filter to "kick in" as close to the highest audible sound you want to hear.
Second, lets talk about the software.
The main idea of operation here is to provide a differential PWM (pulse width modulation) signal to the gates of both half bridges. We use the PWM to generate an approximation to the sound we want to deliver to the speaker and the filter smoothes it out in order to make it sound better. In the case of our design, we were lucky enough to have a differential PWM output on the MCU (micro controller) we choose for the design. This make things easier for us to develop and also prevented the introduction of extra hardware.
So, why should all this matter?
Because we can use this exact circuitry to drive any speaker(s) and it will perform the same. This allows us to hack the base to drive a pair of headphones instead of a single speaker quite easily. In the following pages you will see that it doesn't take much to get your Base headphone enabled. Just a little patience and hot glue!
Note: I do want to make a note here that you cannot use the headphone jack as a line in. There are lots of reasons for this but the biggest is that the circuitry isn't capable of taking in outside signals. (It is only able to send signals out)
Ready to tear things apart? Lets get started!! If you're interested in leaning more about this circuitry you can read up more at Wikipedia. I also highly recommend on checking out Mark Feldmeier's (a very good friend of Sifteo) website about everything PWM audio. There is also a decent white paper that TI released discussing more on the topic as well.
It's go time.
Step 3: Liberate Stickers
Method 1: Using a sharp implement peel up one of sides of the sticker. Then, with your fingers, pull the sticker the rest of the way off. This method usually results in ripped stickers and I recommend (if you have the tools) Method 2.
Method 2: Again, using a sharp implement and a heat gun/heat source, peel the sticker from the Base's plastics. I prefer this method because, as long as you're careful, the stickers stay intact and usually can be stuck back on afterwards. I chose a setting of 100ªF (the coldest the heat gun can go) and keep the blower speed on medium.
Step 4: Extricate Printed Circuit Board Assembly
I've outlined what needs to be done into some sub-steps:
1. Remove the top plastic "grill" from the main body.
The best way is to get your fingernails underneath the plastic and pull. As long as you have removed the screws in the previous step it should pop off freely without much force. Be careful as to not pull too much, the speaker is still attached via two wires. We'll remove those in the next sub-step.
2. Unsolder the wires.
Fire up your trusty soldering iron. We're going to un-solder the wires from the speaker. It makes it much easier to work with the printed circuit board assembly (PCBA). It may be easier to remove the wires from the PCBA after you have followed sub-step 4.
3. Remove the screws holding the PCBA in the main plastics.
4. Remove the PCBA.
Now with your pointer finger pry the PCBA from the base plastics where the round hole is in the printed circuit board (PCB). You may need to give it a good tug to expel it from its previous home.
Nice, the disassembly is complete. Now comes the fun part.
Step 5: Lets Go Crazy
If you have chosen the red pill, let us continue:
Cut the built in stand off:
There is really only one good place in the base where we can stick the headphone jack. It is in the back to the left of the battery compartment and USB connector hole. The plastic standoff must be trimmed about halfway in order to fit the stereo jack in place.
Step 6: X Marks The Spot
I've placed an X on the assembly illustration where the headphone connector should be glued. The metal prongs should be facing up and the the hole (where you insert a headphone jack) should be facing out toward the edge of the board. The hole should be flush with the edge of the board as well.
Step 7: Soldering is like welding, right?
Now that the headphone adapter is firmly glued in place we can make the electrical connections! By removing the wires in step 4 we paved the way for new wires!
1. Solder the common wire,
Solder one wire from the SPK1 point to the middle pin on the headphone adapter. Try to expose as little wire as possible so they don't short.
2. Solder the left and right channel connections.
Because the signal we produce on the Base is intrinsically Mono sound we need to short both the left and right channel so we can get sound in all speakers. Solder a wire (or wires) from the bottom SPK- point to the left most and right most pin.
Thats it! The hard part is almost over!
Step 8: Test It
1. We've cracked open the guts of the Sifteo Base
2. We've unsoldered the speaker wires from the speaker and the PCBA
3. We've extricated the PCBA from the plastics
4. We've performed minor surgery on the plastics to the headphone adapter can fit.
5. We've glued the headphone adapter in place.
6. We've made the necessary electrical connections as well.
Now that we've made some electrical connections let's test this bad boy! The fastest way of testing this is to carefully plugging the PCBA into USB and plugging a pair of headphones in. The Base should turn on and play the startup sound.
Warning: the BTL circuitry drives your headphones extremely loud. (i.e. it could damage your hearing). Make sure the volume is at least half volume before continuing.
Also, make sure you plug the headphone jack all the way in. It won't work otherwise!
Step 9: Dive. Dive. Dive. -- Drilling the Holes.
Drill the holes:
I've provided a template 1:1 that will help guide you where to approximately make the hole for the headphone jack.
Note: As long as the hole is not made too high you can adjust the where the headphone adapter sits by adding shims.
Tip: start with the smallest bit you have and work your way up to the largest. it will make it easier to adjust if you start off target.
Step 10: The Foot Bone Is Connected To The..
Quick assembly instructions:
1. Snap the pcb back in place:
At this point, you should reassemble everything in reverse order of taking it apart. Be sure to align the potentiometer slider with the black plastic piece that interfaces it to the main volume slider. (Illustration shown).
2. Screw the PCBA to the plastics:
Use the longer screws to screw the PCBA back in place.
3. Snap the top grill back in place.
This is a good place to make sure everything fits mechanically. If the top plate doesn't sit all the way against the main white body something is amiss!
4. Replace the outer screws.
Note that one of the screws that holds the top plate on will not adhere into the plastic (because we cut the standoff). Do attach the one screw that will still work.
5. Test one last time.
You know what's the worst thing ever? You finish a project only to find out that an integral piece on the inside is broken or not working correctly. I recommend a quick test to make sure everything this still working A-Ok.
6. Replace the stickers.
Now that everything works you can place the stickers back to their respective locations.