Neutrogena light mask part 2: down the rabbit hole

In part 1 I hacked the light mask to get 99 lives. In part 3, I play with the LCD.

Final touches

Since it’s more convenient to use the built in timer (for now) than time manually, I added a programming port on the side so I can reprogram it when I need to:


The connections are CS, CK, MOSI, MISO (not required) and GND.

It’s always useful to have IPA or white spirits (effective but smelly) around to wipe off the excess epoxy on the visible bits to get nice looking results. I made the hole with a drill and needle files.

Further analysis of the circuit

I’m now kind of curious about how accurate my guesses about the functionality were. Also, I have another controller kicking around which is now at 0 uses remaining and has no programming port. So, I pulled off the transistor. First, here’s the  hFE:

Measuring Hfe of the main switch transistor

The transistor meter doesn’t get a lot of use these days

That’s comfortably in the middle of the 160-300 range expected from the datasheet.The transistor tester has obnoxiously deep holes for the legs…

So, what about the stiffness of the regulator? So, it’s driven by a 1k resistor from a 3.3v source through the base. I’ve got a bag of ST Microelectronics 7833 regulators. They’re meant for regulation not references and the tolerances are quite weak, but in practice the regulation is very good. From 4.65V to 27V, it’s bang on 3.20V output. It was a tiny bit worse at the low end (4.65 to 5.5V), giving out 3.19V when it was scorching due to being connected up backwards, but cold it’s even better. Here’s the test circuit:


With TP0 and TP1, I’ll be able to measure both the voltage across the transistor and the current through it.


The resistor is a whacking great 10Ω beast from some old board I found in a junk pile at my old cow-orking space:

A circuit board maybe off a UPS

Two of the white ceramic rectangles are 10Ω, 10W resistors. The black column in the lower right is a high power 300Ω resistor. Those relays look beautiful and I want to use them for something.

I find having a junk pile of old boards good. Partly I find that despite being able to easily buy the parts I need, I often don’t think of them until I need them at which point I’d in practice have to wait until the next weekend. Having a pile of oddball parts can often yield something useful which works before the weekend expires. Also there’s something satisfying about getting use out of landfill. And then there’s the nostalgia trip: when I was a kid, many of my components were rescued off old junk boards.

There’s a bit of a knack to removing large parts, but it’s much easier now I have a half decent iron (it’s only half decent, but better than a 25W fixed temperature one!). Setting it hot (426C) helps, of course due to the thermal mass. The other trick is to add lots of extra leaded solder. This dilutes the unleaded stuff lowering the melting point and helps thermal coupling of the iron to the joint. Also, having a moderate amount of solder seems to work better with solder suckers. It’s counterintuitive to add solder when you want to remove it 🙂

The resistor is a Dale (Vishay now) 5% 10Ω wirewound ceramic cased one. Worth a couple of quid new. A nice part from a good manufacturer.

Back to it

Hmm, no that’s not quite going to work. Even at 4V, we’ll push 400mA (the expected value) through the resistor, which may correspond to as little as 4.2V total if the transistor is well saturated. That’s below what the 7833 can regulate; unlike the one on the light mask it’s not LDO (low dropout). Looks like we’ll need two PSUs. Fortunately I have ALL the wall warts. This one (actually a brick not a wart) comes from an old IDE hard disk enclosure of 2008 vintage and gives a good 1.5A at 5 and 12V. Off comes the 5 pin mini DIN and on goes a header suitable for a breadboard or other similar socket:

I always find it’s worth doing things properly: I added a rigid strain relief and insulator using some polycaprolacetone derived plastic. It will stop shorts and annoying breakages.

The modified circuit is now this:


And I also put an ammeter in series with the base. It’s current-ly (heh heh heh) running at 2.49mA. I reckoned 2.7 before, so that’s not a bad guess! I tried a manual voltage ramp using my power supply, but it’s too slow: the transistor heats up a LOT, so the base current increases a lot too. I guess that’s part of the circuit stiffness in a sense, but I want a roughly constant temperature ramp if I can get it.

New circuit time!


I’m using an Arduino for doing the timing. It has a very short duty cycle (0.1%), so instead of dissipating somewhere around 10W, the whole assembly will dissipate 10mW or so. I guess I probably don’t need those power resistors after all. The switching is done using a N channel MOSFET (2N7000) to switch a high side power P channel MOSFET (IRLIB9343). The switch going on causes the 100μF capacitor to charge, rapidly ramping the voltage across the assembly under test, then it goes off, causing it to rapidly ramp down. Given the values, the time constant is around 1ms, so the whole test should be finished in 2-3ms or so (I’m wrong! more like 6-10ms).

The circuit’s been running a while and nothing is warm, and the base current is steady at 2.51mA, which is excellent. This is also where I love having a good 4 channel slope. I’ve set the scope to trigger off the Arduino, giving a very nice trigger. I then set it to averaging mode, to give very clean traces:


Channel 1: V1, Channel 2: Arduino, Channel 3: Vt

Plotting Vt against I=(V1 – Vt)/10 gives:


Yikes!! That’s one hell of a lot of hysteresis and the voltage goes negative??? It is however pretty decently stiff especially on the return leg. There are a few clues knocking around indicating that there’s a problem with my building of the circuit, rather than the hysteresis being due to the device under test. One is that it, well, goes negative. Then there’s a very sharp drop when the switch turns off, far faster than the discharging. And finally, the Arduino voltage takes a very long time to settle back to 0V.

Nonetheless even with this measurement we’re getting 20% regulation of current between 1 and 7V. I think the return leg is probably more accurate since it’s going slower so there are fewer transient effects. That’s more like 10% regulation.

I think the main reason is likely that I’ve been awfully lax with where I’m taking the measurements, see:


Left: the circuit, right: labeled. The power traces are in red and black. Scope probes are labeled in the trace colours (yellow, V1, magenta Vt, cyan Arduino) with ground as grey. The component under test has a white square around it.

The currents are biggish (half an amp or so) and the breadboard trace resistance as well as the contact resistance is nontrivial.You can see there’s a fair bit of stuff between the measurement ground and the transistor, especially the relatively high resistance points between the wires and pins and the breadboard. There’s quite a bit in the way of the bulk storage capacitor too, which explains the slightly wobbly traces too. The solution is to move the measurements right onto the legs of the transistor:


Left: the circuit, right: labeled. The power traces are in red and black. Yellow: V1. Magenta and green are both nominally Vt but green is soldered to the resistor leg and magenta to the transistor leg with no power flowing through the measurement wires. Cyan is the trigger as before. Grey is the scope common and is now soldered to the transistor leg too. There’s also a 1000uF capacitor placed very close to the high current circuit in the centre of the board.

Because of that there’ll be some unknown trace and contact resistance in series with the current sense resistor. I can solve that by making use of the fourth scope probe which will interestingly tell us something about the breadboard’s resistances. If it’s less than 0.5Ω then it’s within the tolerance of the resistor anyway. And while I’m at it, I’ll bump down the delay between measurements to 0.1s (100mW dissipated). That way I can actually get all 1024 measurements in the average without quitting early due to laziness. Here are the very clean looking traces:


One thing I didn’t really note before which you can see is that the decay curve doesn’t look very exponential: it’s actually pretty flat especially at the start: precisely what you”d expect from a constant current sink. The analysis gives:


Well, that’s disappointing. It’s basically the same. There’s less noise (due to more averaging) and it’s slightly smoother, but the hysteresis is still there almost unchanged. I doubt at the moment that it’s a transient effect in the device (e.g. thermal). Suspiciously, the discharge leg which is slower looks better. My current (this is a pun as you will soon see) best guess is that the base drive (see?) is taking a dip, because resistance between the emitter and the ground rail causes the emitter voltage to rise relative to ground, so the base current will drop, maybe until some capacitance charges up?

I’m not sure. The options are to measure the base current (there’s a roughly 2.5V drop across the resistor, which we can measure with the scope), and if there’s a flaw there, then I can stabilize the base current either by changing the drive circuit ground to a different place (e.g. the emitter measurement wire—it’s only a few mA) or sticking a high inductor on the base to resist transient changes in current.

The easiest thing to test is to change the width of the on pulse (and the capacitor) up and down by a factor of 10 to see what if anything changes. That should reveal a lot about the nature of the transient effect.

But first! I can check to see what the board and joint resistances are, using the extra probe that I added. I know the current from the big resistor, and it should be a simply V-vs-I plot…




Temporal tests

Where was I? (there was around a 3 week gap here, so I’ve kind of forgotten). Oh yes, I was going to try varying the pulse length by a factor of 10 up and down. I’m currently using a 1ms pulse (the shortest available with delay() on the Arduino) for which I need a 100μF capacitor. I’m going to go for 10ms and .1ms as well. So, I have to replace that 1000μF with a 470μF one, since apparently I’ve run out of 1000μF capacitors and that’s my last one. Okey dokey then. Also, during these experiments, I tweak the power supply voltage so that the voltage across the transistor. I also had to bump the time up to 15ms for the slowest setting. By the time I got to the 10μF delay, I had to turn off interrupts and switch to delayMicroseconds(95), in order to get a 100μs delay. I also noticed some gnarly ringing, so I added gate resistors to the MOSFETS and a 100nF capacitor to the timing cap to take the edge off. Even so this is a hell of a fast circuit for a breadboard. Without the gate resistor, the gate of the 2N7000 has a rise time of about 20ns.

I also connected it up wrong, slightly smoked the DUT and burned my finger. Amazingly, it still seems to be in full working order. Ouch ouch ouch ouch. Anyway (ouch) here’s the traces:


No perfect, (ouch) but let’s see how the V/I cures look:


The legend indicates the capacitor used. That corresponds to pulse widths of 15ms, 1ms, 100μs and 10μs.

Well, that’s  lot better!! Those long pulses have awful transient effects, sine the power draw is high. As the pulse shortens that goes away, and the hysteresis cure closes up. I don’t believe that overshoot however on the quickest curve. I suspect I’m getting a different sort of transient effect there.

Also my PSU has now become unstable above 24V out. Naturally I need about 26 for this setup. Whyyyyyyyyyyy???

But that regulation is not bad (5% over quite a wide voltage range), or would be if the circuit actually hit that range. It is serving as a decent upper limit on the current, I guess, using only very cheap components and what was already required for other things (the 3.3V regulator).

More on transient effects

I’d still like to reduce the size of the hysteresis loop. I speculated that the base current had something to do with it too. The circuit has no star ground and has pretty high currents. Due to the voltage drop along the ground rail, the regulator circuit will probably drift up and down. So, I’ve measured the voltage on either side of the base resistor. Using the scope’s maths functions (through a truly interesting interface), you can see (red channel) what the voltage fluctuation over the base resistor is.


As usual, blue is the trigger, and yellow is the capacitor voltage. Green and purple are measured either side of the base resistor and red is the difference between them. It’s a much smaller scale, so very very noisy. The temporal averaging really helps here.

That’s around a 5% change, which is certainly significant. Inductors resist change in current, so I’m going to stick a big inductor (if I have one) series with the base resistor to stabilise the current. The old PSU board has a transformer on it. I’m going to take that off and see how it looks.

Wretched device was press-fit and solered, so I almost busted it trying to take it out. The transformer has two sides: 1.6Ω/5.4Ω with inductances of  13/35mH, which is somewhat less that I expected. And that made little or no difference. That board also has a whacking great Omron LY4 relay which has a coil of a more respectable 3.5H, with 350Ω nominal resistance. Here’s the result 10th a 100μF timing capacitor:


Same as before, but looks like I got bored waiting for the averaging to finish, so the red trace is noisier.

It’s much better, but not quite as better as it looks because the current is being measured as voltage across 600Ω, not 1kΩ, so it’s more like a 33μA rather than 160μA, which is still a huge improvement. The VI curve is:




Yeah, so that’ll teach me for being lazy (no it won’t). Turns out it’s a 120V relay, not the 24V model, so the coil has a resistance of 1.7kΩ, which I would have known if I’d measured it. I have another relay with the specs of 750Ω/1.35H.


Still a 100μF timing capacitor.

Well, that’s a little bit better. As one might expect, it’s better on the outward leg, which is where the majority of the variation was. I strongly suspect I won’t be able to get much better than this without making the circuit on a board that allows substantially better design. For fun, here’s the one with the apparently optimum timescale:


10μF timing capacitor (100μs pulse width)

You know, that’s actually not bad!

Edit: I forgot to include the final circuit diagram, so here it is:


The circuit excluding the 7833 regulator and the power supply decoupling capacitors. Note the inclusion of the major board resistances (RBOARD), and the power resistors with 4 point measurements. I’ve also put the relay in in full.

Conclusions (i.e. tl;dr)

  1. I burned my finger (ouch).
  2. The regulation is decidedly OK.
  3. The user of the transistor was indeed a clever hack.
  4. Measurement is hard.
  5. This was a very long post.

Today’s hack

Let’s say you’re automating a git workflow for a variety of good and bad reasons. Commits are fine, you can just do a:

commit -am 'a message'

and it goes through non interactively. Now let’s say you have a merge and you try:

git merge

It pop open an editor window to let you type a message. There’s no merge -m option to let you provide a message. If you look closely, you’ll see that the editor window already has a message filled in saying it’s a merge. This means if you save without exiting, git sees a message and decides all is OK and it can proceed. So all you have to do is provide an “editor” which quits without saving every time. The program which does nothing except exit successfully is /true so you can simply do:

EDITOR=true git merge

for a non interactive merge.

I don’t know whether to be proud or ashamed, but it works.


louder, Louder, LOUDER! (or: more dead bugging)

Sometimes someone makes a chip to do just what you want.

I’ve recently been needing to generate beeps from a BLE113 module (it’s a CC2541) which runs off a CR2032 coin cell at a nominal 3V, but more like 2 to 2.5 in practice. The speaker of choice is a surface mount piezo sounder which are small (9mm square) and unlike the discs don’t require mounting on a sounding board to get sound out. I’ve not idea if those Murata ones are the best, but it’s a respectable brand and those are the first I found that seemed to meet the spec.

They’re not especially loud, only 65dB at 1.5V pk-pk. The microcontroller I’m using has 4 useful channels on timer 1 for this application, and of course the outputs are totem pole outputs. So, driving it with two PWM channels in opposition is driving it with an H bridge which gives the full 2-3V pk-pk swing (depending on the battery voltage).

That makes it little louder, but not an awful lot. The datasheet says that the sounders can be driven at up to 12V pk-pk without damage. The datasheet however merely notes that it is “probable” that increasing the voltage will increase the volume, which is a bit unhelpful, though it has a graph for one (not the one I want) showing an increase with voltage exactly as you’d expect.The question then is how to generate a higher voltage for the buzzer. I had lots of ideas:

    Boost / switched capacitor converter and another H bridge (impractical–too many components)A miniature transformer (none quite small enough or with the right turns ratio)A miniature autotransformer (closer, but still the same problem)Something cunning with an inductor—some sort of ad-hoc boost thing which generates spikes rather than a square wave. Idea not really fully formed.

None of them are really any good. They’re either require impractically large number of components, components that either don’t exist (or I can’t find) or are vague and ill formed and I don’t have the parts to test the idea and anyway I’d probably end up busting up the chip with voltage spikes.

Fortunately it appears that someone thought of this already. It turns out the PAM8904 already does exactly this. It’s a switched capacitor converter with an H bridge, that takes a digital signal in, precisely for the application of driving piezo sounders from low power microcontrollers. Which is nice.

Except I’m not very trusting, and I’ve no idea if it’s worth the effort. I don’t want to order a circuit board and then fiddle around hand soldering QFNs (I’ve seen it done, I’d rather use a stencil) for a one off test. Like so many chips, it’s QFN only now. So the obvious thing to do is to buy one and deadbug it.

I figured I’d try the nice fine hookup wire I’ve got. The colours make it a bit easier to follow which wire is which. Next time, I’d try the same soldering job with enamelled wire. It’s harder to strip and tin, but the insulation doesn’t get in the way. The key to getting the soldering to work in the end was to tape down the wires with masking tape (3M blue tape) as I went along. Even with that it’s two steps forward, one back as you accidentally desolder wires when trying to attach new ones. Here it is!


(OK, not as good as this, or this, or this—hey that socket is a really nice idea!)

Spot the schoolboy error? I remembered to check continuity between neighbouring pins, but I forgot to pot it or otherwise protect the wires and so some of them fell off when I tried to change the boost voltage selection. And then another 4 wires fell off when I was taking it out. The connection area is tiny and the solder work is frankly not that good, so the joints are amazingly fragile. It’s what I should have done first time, doubly so because the bits of stiff wire for the breadboard really get in the way.


Well, it seems to operate correctly, but I think I’d do it differently next time. A chip socket or veroboard with .1″ header soldered in is a much better choice than flying wires. Potting makes it as robust, but you have to pot it before you know it works.

It’s always a bit hard to tell volume because ears have a logarithmic response and at 4kHz the sound is quite directional. Nonetheless it’s noticeably louder. Yay 🙂



Good job, TI, I half mean that

I was a little surprised today when trying to debug a board when one of the output voltages was 4.8 V. The main reason for the surprise is that the power supply is specced at 3.3V. And I didn’t make the supply, Texas Instruments did. In fact it’s one of these.


Checking the manual reveals that TI do indeed claim that it’s supposed to output 3.3V. Time to find the regulator! There’s no continuity between USB power and the output so it’s not a short. Poking around on likely looking chips quickly reveals that the regulator is OUCH THAT SUCKER IS BOILING HOT! this one:


And has the markings in very small “PHUI”. I got a far as googling “PHUI v” before it autocompleted to “PHUI voltage regulator”, so I guessed I was on the right track :). Not very further down the track the TI TPS730 datasheet crops up showing it’s a TPS73033, which is a 3.3V LDO regulator rated to 200mA. And did I mention it’s baking? It seems to be fried in a rather unfortunate mode (and just for good measure, the NR pin which ought to be at 1.22V is at 0.14). Also, it turns out that the entire circuit diagram was in the manual, so there was no need for that bit of minor sleuthing.

So why good job TI? Well, the other, much more important chips, such as the micro controller I’m programming are rated to 3.9V absolute maximum and it didn’t die with 4.8V across it. I’m pretty pleased about that, because I can imagine going round a cycle frying many chips before finding out the power supply was defective. :shudder: :(.

Well anyway, it’s fried and I can’t use it. I mean technically I’ve successfully programmed the chip and not fried anything as far as I know, but there’s another as yet untested chip on the board rated to only 4.8V absolute maximum. I can’t trust it, so I can’t use it and so as far as I care it’s broken.

And that means I’m free! This guy has a great philosophy which is that if something is broken then there’s no risk of breaking it so you may as well try to fix it. Fortunately, I have some old boards which I’m not currently using which have ST Microelectronics L78L33 SO-8 voltage regulators on them. They’re not LDO so getting 3.3V from 5V is a bit dubious and actually is not quite within spec, but whatever, both my chip and the one in the programmer (a CC2511) work all the way down to 2V, so I reckon that is won’t matter. Also, it’s only rated for 100mA, not 200mA like the original, but both the chips are low power wireless ones so I doubt the current will go too high even when it’s programming. And besides that won’t be for long.

Time to dead bug it! And pot it in hot melt!


And it works! 😎

The LED perhaps to the surprise of no one is dimmer than before and the output voltage is 3.2V which is in fact well within spec for the 7833.


Hacking the “Double type 12000” vacuum pickup tool

A while back, I bought a vacuum pickup tool as such things promise to make SMD work easier than with tweezers. The pickup tool is circular which makes it easier to rotate in your fingers and it picks up from the top, so you can’t accidentally dip it in some of the solder paste making it sticky.

I bought one of the ubiquitous “Double type 12000” pickup tools off ebay. They’re cheap (£20 including shipping), and much like the 852D+ rework stations, they seem to come in a variety of brands which have nothing different except the label. If you like yellow, get the “VAC” brand one, but if you prefer pink, get the “Cosmo” brand one.

They comes with two suction ports, two pickup wands and a selection of tips and rubber suction cups.The wands are connected via transparent hosing which looks like that aquarium hose, but is rather thinner walled and much more flexible.

Double Type 12000 vacuum pickup tool

A slightly out of focus and badly lit picture of the tool in question.

I tried to use it it and… it sucks (sorry!) but isn’t very good. There’s a small hole on the pickup tool: cover it with a finger and you can pick up things. Uncover it and they drop off. There Are two problems with that. Firstly, I found it completely unintuitive, since the operation is “backwards”. I dare say you could get used to it with sufficient use. Secondly moving your finger disturbs the position slightly, so just as you release, the position goes bad, which is the worst time for it. As a result, I found it unusable and went back to tweezers.


Apparently the good ones operate off foot pedals, so it’s time to add foot pedal control to it. So, I got a foot switch and a couple of cheap solenoid valves and a T adapter off ebay. One claimed a working pressure of 0.02 to 0.8MPa, which seems a bit too high for this pump, the other had no specs. But they were only a couple of quid, so I figured, what the hell?

Aside: every time I buy some of these random goods from China off ebay I’m astonished that it’s worth someone’s time to manufacture a valve/footpedal, sell a single item, package it up and send it half way around the world for £2, when the manufacturer, vendor, ebay, creditcard processor and post office all need their cut in order to turn a profit. The efficiency of the system is mind boggling.

The idea is to connect the solenoid valve to the hose such that opening the valve exposes it to the atmosphere, killing the partial vacuum inside. So, I connected it all up (minus the foot pedal which is yet to arrive)…

Valve connected to the tool

Valve connected to the tool. Yep, the hose is bodged into that port with tape.

Oddly enough it kinda-sorta works. By powering off and on the solenoid, I can pick up/drop quite large things. However I can only pick up small things, I can’t drop them again. This implies the internal resistance of the valve is very high so that it lowers the pressure a bit, but not enough. Time to delve in and figure out why. Firstly the valves in question:

Tow very cheap valves

The two valves.

These valves are really very similar. The solenoid are almost identical, but not quite (one’s 12V, the other 24V as it happens), and the connection from the solenoid to the valve body have the same form factor, so they’re interchangeable.

IMG_20151112_193247 IMG_20151112_193303Guts of the valve

The valve itself is a simple,  cunning design. It has an internal rubber diaphragm with a rigid plastic backing that serves the dual purpose of acting as the switching component as well as sealing the two halves of the valve body together. The core of the solenoid is inside, the sealed part. One of the two valves has an additional spring (shown) holding the diaphragm down weakly, in addition to the spring weakly pushing the solenoid core out. Note the arrangement of the valve internals: the fluid enters from the right and exists from the left. There are also two very small holes in the diaphragm. The top of the solenoid core is squishy plastic and when off, the core seals the middle hole by pushing against it.

Now imagine there’s pressurised fluid coming from the right. This leaks into the top half of the valve and pressurises it. The outflow is at low pressure, so this pushes the diaphragm down, sealing the valve. Now the solenoid opens. This opens the middle hole and the fluid in the top chamber leaks into the outflow. The two holes are very small, so there will be a substantial pressure drop across them, meaning the top chamber now has half the pressure of the input fluid. Looking at the arrangement of the chambers in the bottom of the valve, this means that the high pressure fluid coming in will push the diaphragm up, allowing fluid to go from the entry to the exit.

This is a very cunning arrangement is essentially an amplifier because the solenoid is a bit weak on its own to do much. It also explains the behaviour seen above. The valve needs substantial pressure to operate. Not only that, it must always drop a fair bit of pressure across the body too, which means it also needs substantial flow rate. The pickup too has neither, but the leakage which happens when the valve is open lowers the pressure enough to drop large parts but not small ones.

The solution is to rebuild the valve to turn it into a needle valve which can operate at very low pressures and flow rates.

Rebuilding the valve

Rebuilding the valve.

First, I drilled out the central hole to about 2mm diameter to increase the air flow rate. I then put a 3mm shaft (back end of a drill bit) and filled the top with molten polycaprolacetone (low temperature thermoplastic). The 3mm shaft keeps the hole open, but it’s necessary to wet it with slightly soapy water (soap aids the wetting) so stop the plastic from sticking strongly to metal. I then removed the shaft and flared the opening of the hole. Flaring is important since the core can move side to side by around a millimetre and so it needs to be guided into the hole. I then pushed the solenoid core in gently, so that the top section of the hole matches the profile of the core perfectly. Removing the core, you can just see the lip on which it will rest inside the hole:

Rebuilt valve body

Rebuilt valve body. I initially used a pencil to try to flare the opening. The red stuff is the paint that the plastic pulled off the pencil.

It’s also necessary to then drill out the second hole so there’s somewhere for the air to go once it enters the top chamber. The result works extremely well. The solenoid valve can now e used to pick up/put down very large and very small parts without altering the speed of the pump. This indicates the air flow rate when open and sealing when closed are both very good.

The end result is it works pretty well. Once my foot switch arrives, it will be complete and usable.

Edit: Well, that blows!

While playing with, I observes something very interesting. When the valve is open the pickup tip actually blows air out of it! My complete speculation is that while the pump is sucking (it’s oscillatory), little air gets drawn in due to the high resistance. However, a lot of air gets pulled in the valve tube. This air has momentum, so when the internal valve on the pump closes and it stops sucking, then moving air has to go somewhere, and out of the end of the tip is the only option.

It’s very gentle (not enough to disturb SMD work), but it is an amazing effect, and probably will help the tool drop very light things even if they’re slightly sticky.


Edit 2: My foot pedal isn’t here yet 😦

Well, my foot switch still hasn’t arrived and I’ve done every part of the project I can without soldering up my circuit boards.

Foot switch hack.

The solution is one absolutely appalling hack. I made a foot switch out of a sponge with a hole cut out of it, some old circuit boards with a Prym 13mm snap button stud soldered to one, wires, and of course duct tape. It works fine since the 24V solenoid only draws 200mA at its rated voltage.

It’s horrible and looks like something I might have made in junior school. It does work and once compressed to the right depth is remarkable easy to control.


Edit 3: I tried it and it’s fantastic!

The new foot switch controlled pickup tool is a complete game changer compared to using tweezers. I had to solder a board full of closely packed 0402s and 0.5mm pitch DFNs. I couldn’t imagine doing it with tweezers.

Actually I can, and I’m REALLY glad I have this tool now.