What is the # of this chip

[kinarfi]

I have an "Air Leggy" air pump leg massager that runs continually when on, that is, it pumps up some air tubes wrapped around my leg and compresses them for 27 to 99 seconds, then deflate for 3 to 11 seconds, depending on how many times I push the up or down button after I turn it on. I'm hoping to modify the existing PCB so it can compress for a certain amount of time and then deflate for 5 - 10 minutes instead of 3 to seconds. The attached is a photo of both sides of the PCB and the motor and valve with the back side of PCB photo being flipped to match the front side with the components drawn in. Does anyone have a guess as to what the DIP8 chip is?

 

[Brevor]

My guess is a PIC 12F series, something like a 12F629.

 

[Mr RB]

Yep, the power pins and pin4 GP3 MCLR pin all match a PIC 12F series.

Since it does not appear to use an ADC input (ie 12F675) a 12F629 would be my best guess too.

 

[jpanhalt]

Why do you rule out the 12F5XX chips? Can you tell from what is given that there is an interrupt?

John

 

[Brevor]

Why do you rule out the 12F5XX chips? Can you tell from what is given that there is an interrupt?

I wasn't actually ruling out the 12F5XX chips, I said SOMETHING LIKE the 12F629.

 

[kinarfi]

So if I want to change the on, compress, and off, deflate, times, what suggestions are there, I'm thinking an on time of 1 to 2 minutes, because of the longer deflate time, and a deflate time of 3 to 5 minutes.
If left up to myself, I would use a simple 555 timer.
Thanks
Kinarfi

 

[jpanhalt]

If left up to myself, I would use a simple 555 timer.
Thanks
Kinarfi

The 12F series can be programmed to emulate a 555 timer (https://www.hightechips.com/). In case you want to give that a try. Just be sure to remember that Pin8 is power and Pin1 is ground in the 555.

More to the point of changing the inflate and deflate times, since the company went to the bother of removing the chip's identification, it probably protected the program. That will mean you cannot easily read the program and manipulate it. It would be easier to start from scratch.

And finally, my earlier comment was referring to post #3, not post#2. Tying pin 4 high is suggestive that it is a PIC, but I don't believe the PICAXE-08Mx is ruled out. I imagine that by price alone, the PIC 12F would be favored.

John

 

[kinarfi]

Thank you gentlemen, since I have not learned micro processors yet, I think I will try going with 555,
I appreciate you help!
Kinarfi

 

[Mr RB]

Why do you rule out the 12F5XX chips? Can you tell from what is given that there is an interrupt?
...

I'd still lean towards 12F629 as the device looks to have timing/flashing requirements and buttons which are easier with interrupts, also the price difference is not that great between the chips compared to the loss of features.

Many manufacturers would go for the slightly better spec chip as they an use it in a number of apps and get the bulk pricing benefits rather than source smaller quantities of different spec chips.

But as you said there is no ruling out the other 12F parts, only wild guesses by us.

 

[MrAl]

Hi,

I tend to agree with the other poster's here that is could be a 12F type PIC chip. It's not certain, but the pinout seems to match that required to use a 12F chip. In other words, it would probably be possible to unsolder that chip and replace it with a 12F675 chip for example with your own program in it and have it work the same as the original. This is one way to do it actually, but you'd have to either program it yourself or ask someone here to program one for you. The cost of the chip is less than 2 dollars plus mailing whatever that costs to your area.

As to reading the original chip identification number, sometimes it is printed so lightly that it is hardly readable without a good magnifying glass and light angled just the right way. But if they did in fact remove the writing then you cant get the number without writing to the company and asking if they would reveal it, or else finding a schematic on the web. If you do get the chip number you might be able to read the program code but it might be locked. If it is locked you cant read it, but if it is not locked you can read it but you still have to be able to reprogram it which again requires knowing how to program these chips and also obtaining a programmer board.

So i guess if you know how a 555 chip works and you know it will work to use one in this application then maybe that's the best way to go. At least you can get it to work without too much trouble and if you want to experiment with the timings you can do so quite easily.

Also, if you care to trace out the schematic and draw it in it's entirety we can take a look and make more recommendations like how to arrange the 555, unless you want to do that yourself anyway.

Good luck either way you go with it, and if you care to get back here with your results we can read about it. Pictures are nice too if you care to take more and post here

 

[jpanhalt]

Hi,

As to reading the original chip identification number, sometimes it is printed so lightly that it is hardly readable without a good magnifying glass and light angled just the right way.

Another trick is to add an oxidizing acid -- I prefer nitric -- strains, etc. in the epoxy from the original impression may be revealed that way. I believe that would all be for naught, though, for the reason I stated above.

A single 555 may work in astable mode, with a relay, if you can get a 4 to 7 minute period with a 70% duty cycle. Of course, the shorter the period, the easier it will be to select components. I did not actually test whether those timings met the datasheet's minimum current requirements. A better definition of what you need in terms of on and off times would help.

John

 

[kinarfi]

I agree that the chip is a micro processor and as I said earlier, I don't know them yet. It appears that the chip has several set time on time off settings and the up & down buttons choose the time. Problem is that the off time is not high enough, my lower legs were disabled by a crash and I now have restless leg syndrome and I think it's caused by blood pooling in my legs and the system only needs to activate once every 5 to 7 minutes and from 0 to full charge takes about 60 seconds and with a hold of 30 second, then 5 minutes rest.
It also appears that the out puts simply turn on the transistors to drive the pump and valve. Should be easy to replace the micro with a 555, even if I just dead bug it.
Question, is there a reason for powering the chip the way they did?
Kinarfi
OOPs missed the series resistor for the LED

 

[jpanhalt]

C2 is probably not needed at the low frequency you plan. A value of 10 nF (0.01 µF) is more typical when it is used and is recommended in the datasheet.

As for the MCU power, I assume you are referring to R3,R4, C3, C4, and D3. That design is to decouple the MCU from glitches produced by the motor and solenoid. Think of a low pass filter. You will need to include decoupling too, but it is understandable that you left it out for simulation.

Are you sure of the orientation of D1 and D2?

John

 

[kinarfi]

C2 is probably not needed at the low frequency you plan. A value of 10 nF (0.01 µF) is more typical when it is used and is recommended in the datasheet.

As for the MCU power, I assume you are referring to R3,R4, C3, C4, and D3. That design is to decouple the MCU from glitches produced by the motor and solenoid. Think of a low pass filter. You will need to include decoupling too, but it is understandable that you left it out for simulation.

Are you sure of the orientation of D1 and D2?

John

Right you are about C2 on the 555 drawing, not needed and it should be 10pf if used.

Thanks for the advice on the MCU power and I will incorporate it when I build the 555 version. I really didn't leave it out, as it is one of those little practices taught in theory and learned by practice, and it's been long since I was "taught" and never practiced that particular idea. - Thanks -

Yes, I do believe that D1 & D2 are drawn correctly, they are there to shunt spikes to ground when the pump and the valve de-energize.

Kinarfi

 

[jpanhalt]

Right you are about C2 on the 555 drawing, not needed and it should be 10pf if used.

I believe you have your picofarad (10E-12) mixed up with nanofarad (10E-9); 0.01 µF = 10 nF.

Yes, I do believe that D1 & D2 are drawn correctly, they are there to shunt spikes to ground when the pump and the valve de-energize.

Kinarfi

I don't think so. Take Q2 and D1 for example. When Q2 turns on, D1 will be forward biased at near its maximum rating, assuming a supply of only 5 volts, for at least a minute. At best, it will get hot and reduce power to the motor (the motor will see only the voltage drop across the diode). As snubbers for inductive kick, they should be reverse biased (i.e., turned around). The shunting is to the V+ supply. That is, the kick has opposite polarity. With an ohmmeter, check the circuit you have again.

John

 

[kinarfi]

Yes, you are correct, I do have them drawn correctly on the photos, but not on the drawing, and yes, I misspoke. pico is 10 to -12, nano is 10 to -9, micro is 10 to -6, and mili is 10 to -3, I know that, but my finger don't
Now then, How many errors and what suggestions do you have for this design?
Please and thanks,
Kinarfi

 

[jpanhalt]

I did not run the simulation. It does not appear that you have pin 8 of the 555 connected to Vcc. Also, it looks like both of your control transistors turn on and off at that same time. Remember that the 555 can source and sink.

One way to alternate the two controls (compressor and deflator) would be to use a PNP transistor with a pull up on its base to control one of the devices. That is, when the output is low, the PNP would be one. When the output is high, the NPN would be on. Using the CMOS version of the 555 will get you closer to the positive rail voltage for turning off the PNP. You can also just use a double-throw relay (i.e., one with N.O. and N.C. contacts).

John

 

[kinarfi]

Here's what I have in mind to do. Pull the micro chip and replace with NE555, cut some of the traces and add a few component and a few wires. Pin 8 has that low pass set up, both the valve and the motor operate at the same time, other wise, if the power is cut or turned off while the wrap is inflated, it would stay inflated. Take a look at this attachment and you can compare it to the other attachment if you want.

 

[jpanhalt]

Your approach makes sense to me. It wasn't clear in the original schematic and description that the discharge valve was a hold-close valve rather than a hold-open valve.

Have you considered driving the BD131 directly from the 555? With the MCU, each pin was limited to only 25 mA. The 555 can source or sink 200 mA, which might be enough.

John

 

[kinarfi]

The out put of pin 3 of a 555 is high for a minimum of 50% of the time or more and in this set up it is high for around 81% of the time and the 2N2222 (actually a 2SD471) is used to invert that time
347 sec cycle time, 284 sec high time, 63 sec low time.