black gunk on PCBs?

[a7634]

just wondering if anyone knows, a lot of the newer toys i find i crack open and find there isn't much to bend, and they almost always have this hard black plastic-like chunk in a circle somewhere on the board and the traces definitely go under this chunk... is this there purely to prevent modification or repair? or is whatever is under that liittle blob actually useless and the board actually has no bends? or am I nuts? any info would be great...
~AJB

[Circuitbenders]

Thats what is known as a black blob chip.

Underneath theres a tiny chip that contains virtually all the circuitry for whatever machine it is and the black blob is just a resin coating to protect the chip. Most of the time they are difficult or impossible to bend as theres just not enough of the functionality assessable. You'll be lucky if theres more than the power supply rails, the speaker output  and the control inputs outside the blob. You'll often see a clock speed resistor right next to the blob that can be replaced with a pot for pitch control but thats usually about it.

[djsynchro]

Even though you can only mess with the pitch resistor, you might still get worthwhile results.

A body contact will usually work & produce a cool effect because your body acts as an antenna for hum and you'll get a 50 Hz frequency modulating thing going. 60 Hz if you're in the USA!

Sometimes a body contact to either side of the resistor works, when you bridge it your finger will be a resistor in parallel. If the original resistor is quite a high value then your finger in parallel will very likely have an effect.

[stolenfat]

heres an idea for ya- theres no way to access the bends points under the black blob, if you think about it every place you could get to under there is is accessable via the out going circuit connections.  Try getting a knife or something and scraping the tracing on the board to expose the copper and solder directly to the gash,

[nochtanseenspecht]

yeah okay, but still...
anyway, i got some decent results before by heating the blop up or pour in it with a needle
if you try that, keep your sampler ready, becouse your toy won't survive
but at least you can get something more out of it then just a pitch or a distortion

[10k]

wiring several blob circuits together and using them as pseudo LFOs can be fun,
if you have a cheap 1 or 2 effect blob that will loop if button held is down then try
wiring the piezo outputs to a retriggerable effect of a second blob, then changing the
clock speed resistor of the first blob will retrig second at an easily variable rate.
adding a few more triggers and feeding final output back into the triggering blobs can
result in some weird semi random patterns.

another desctructive bend method is overvoltage, seems to quite often result in
making unretriggerable keyboard matrix blobs (musical childrens books) into retriggerable
ones once normal voltage is reapplied.

[nochtanseenspecht]

that is interesting news, 10k. i guess you did try it, make a line of black blobs in series ?
hehe, you freak ! 
deserve a golden blob for that !

[10k]

heh heh heh, hope i don't fry that golden blob looking for bends and become an emoticonoclast.

i discovered this method when i was tinkering with a no-name 2 part musical telephone toy that i'd purloined from the childrens toybox after hearing how nicely it detuned when the batteries were running down. It had a handset with a 2 button blob and a base with musical numeric keys, a few animal sounds and a jungle siren. The handset is a 2 sample 0v trigger blob, with just a clock speed resistor and piezo. Samples are a dtmf dialling string and ringing tone, both loop until break, with the ringtone having precedence. The base is slightly more complex, blob, 2 resistors, transistor and a small speaker with samples triggered by a keyboard matrix, one of the matrix rows being the +3v line.

i had both blobs wired up to the 2 AAs in the base as the button cell in the handset was shot. i'd found a few distortion and sample pausing bends connecting the transistor to the matrix columns when all the prodding and movement of pcbs caused the one of the wires to the handset's piezo to become disconnected, i touched this wire around with no joy so i started a sample playing on handset and tried again and found it triggered the samples from the base's +3v matrix row when touching matrix columns. i guess this works on +V triggerable blobs because the +V to push first blob's speaker cone forward is enough to trigger the second blob?, i measured with a meter and seemed to be getting 0-2.85Vpp on the first blobs output, with silence being a constant 0 similar to an unsigned sample.

So i added toggles on the handset's button points, pots on the clock resistors, and a rotary between handset's piezo and base's matrix columns / speaker, a very rewarding nights work!

Since then i've also made a blob-tangle from a talking dalek toy, winnie the pooh talking book, and another phone dial/ring blob (this one came from a plastic mobile phone toy on the front of one of the children's magazines - identical blob board, guess they must be pretty widespread). The dalek was a classic even before bending as it has just one +V button which cycles through an array of samples, and when you glitch through them at the right speed it clearly begins to swear. 1st syllable of sample 1, glitch, 1st of 2, glitch, 1st of 3, glitch, etc... == profanity; // hoho.

Another pseudo LFO can be had by voltage dropping an LM386 and using its output to trigger, i found that dropping to between 2.80v and 2.85v (just under the voltage it starts picking up AM and way under its nominal 4V minimum) causes it to start cutting in and out and producing tuneable pulse sweeps. Next time i have a blob session i'm going to try wiring a couple of blobs outputs through the inverting and non inverting inputs of the LM386 so once i stop the voltage drop it'll start amping those, at the moment it's just got a transistor+zener white noise generator going to one of its inputs. i've also got a simple opamp variable sinegen and sine->sawtooth that i might try bolting in somewhere, any ideas?

[nochtanseenspecht]

whoaa you lift the black blob bending to an academic level 
after reading this report, i hardly can wait for my children to grow up, so that i can rip
their black blob toys without protest..
i guess that's what they call midlife crisis 

but serious, did you ever made recordings/pictures of that ?
it reminds me a bit of the furby sequencer, did you see that? hilarious...

forget about the golden blob, guys like you deserve a modular system(+ a filled toolbox)