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Sep 04, 2004, 03:04 PM
Registered User

looking to switch between 2 IC chips

i'm looking for a switch that will allow me to switch between 2 seperate 20 pin IC chips. what should i look for? i've been all over the net looking at suppliers and can't figure out exactly what i need. rotary switches look to be what i want, but i can't figure out the pole/decks/positions info. the switch needs to be able to switch between the chips on a pin-to-pin basis. meaning that when i turn the swich from the first position (chip #1) to the second position (chip #2), that it changes the output from chip 1-pin #1 to chip 2-pin #2. get it? any help would be greatly appreciated. thanx guys.
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Sep 04, 2004, 03:29 PM
Dimension Engineering
Do you need to switch all the pins, or just selected ones? FOr example, how many of the pins are power, ground or simply unconnected? A 2:1 multiplexer like a 74HC157 (or up to five of them, in this case, depending on how many io you need to switch) and a switch with a pull-up on the select line (tie the select lines together) would be a cleaner way to do it than a big obscure switch. It'd also have the advantage of switching everything at exactly the same time, with no debounce issues
Sep 04, 2004, 03:41 PM
Registered User
i would assume that all of the pins need to be switched. the whole project as follows. i've got an astro 109 lithium charger and just bought the IC chip for the 110 charger. switch the two IC's and you've got a charger that'll charge both lipo's and nicad/numh batts. obviously you have to change the chip each time. so i figured that i'd buy a switch and 2 dip sockets and install it directly inside the charger, that way i don't have to disassemble it everytime i want to charge something.
Sep 04, 2004, 03:52 PM
Registered User
If you really want a manual switch, a manual computer printer A/B switch would work nicely. All that I have seen switch 25 pins. Should be able to find one at your local used computer store if you have one. I looked on EBay searching for printer switch and saw about a dozen in the 1 to 5 dollar range (plus shipping). New ones are from $15 to $30. Might have to settle for a A/B/C/D switch that would switch between any of 4 differnet devices. Probably cheaper than buying just the switch from an electronics supplier.
Sep 04, 2004, 04:08 PM
Registered User
i thought about that too, but i'm not sure of any problems i might runto doing the swap. i didn't know if the switch boxes had common pins like comatose had suggested. if they do, it might not work. i dunno, i'll be looking. any more ideas?
Sep 04, 2004, 04:18 PM
Registered Taranis User
Miami Mike's Avatar
If the only difference between the 109 and the 110 is truly the microcontroller chip, then the designers, Bob Boucher and Doug Ingraham, could easily design a new chip that incorporates both programs and lets the user select between peak charging and lithium battery charging. They could offer the chip for sale as an upgrade to present owners of either charger, and they could also come out with a new model that did all types of batteries. They could charge more for the new model even though their cost would be virtually the same as before.

So why haven't they done this already? Why do they instead make both the 109 and the 110? They aren't competing very well with chargers like the Triton, which can charge NiCd, NiMh, LiPo, Li-Ion, and lead batteries, so what's going on here?

I'd think twice before trying this modification. You might cause some damage to your charger, your batteries, or both. This needs to be explored further.
Sep 04, 2004, 04:26 PM
Registered User
it's the same charger except for the programming. i've got my 109 charging my gp1100 nimh pack as i write this. after you swap to the 110 chip, charge and nicad or nimh you want (up to the charger limit that is). i don't see where there's a problem to switch between the two chips. as long as the transfer is done without power and without and pin-jumping, i don't see why it won't work. i'm not the first guy to do this either. there are a bunch of guys who have bought the chip and do the swap all the time. i'm just getting tired of opening the charger every time i want to charge a battery that's of the other program.
Sep 04, 2004, 04:28 PM
Registered User
A few of the very early ones did not switch everything, but they were marked for serial or parallel operation. Starting at least 10 years ago the manufacturers just made one box for everthing and switched all lines with the only common being the shell on the DB-25 connectors that became more or less universal on them. One thing I noticed was that quite a few of the 2 position (A/B) switchs made all thier connections with a PC board, while the 4 position (A/B/C/D) used a ribbon cables to the DB25 connectors.
This would cut the work in half by cutting off the connectors and attaching your plug and sockets to the ribbon.

Miami Mike is right that you might have some problems, but the microprocessor probably runs at a slow enough clock speed that if the wires are kept fairly short then it will probably not be bothered.
Sep 04, 2004, 04:50 PM
Registered User
Mr.RC-CAM's Avatar
It is hard to say if the oscillator will start reliable with the cables (capacitive loading issues). Also, it will be important to ensure that the chip's power pins are enabled before or at the same time as the other signals (switch contact bounce issues).

If you are technically proficient then I have another Idea for you to consider. How about installing both microcontrollers on top of each and then trick the RESET control line on the two chips? In the reset state the unwanted microcontroller will tri-state (float). Some micro's might not like the extra capactive loading on the xtal input, so some experimentation may be necessary.

I used this trick on some simple micro based projects and it was successful. But, your actual mileage may vary.

Sep 04, 2004, 05:02 PM
Registered Taranis User
Miami Mike's Avatar
What numbers are printed on the chips? If there's a paper label, peel it and peek underneath.
Sep 04, 2004, 09:33 PM
now that's a wattmeter...
simingx's Avatar
If it's an EPROM, you can do this:

Solder all the pins together EXCEPT the /CE pin (search datasheets for this)
Lift the 2 /CE pins off the PCB so you get the 2 /CE pins from the EPROMs and 1 pin from the PCB where it originally went.
The /CE pins from the EPROMs go to the 2 outer terminals of a SPDT switch, and the original from the PCB goes to the middle.
You might want to pull one of the /CE's down with a resistor so the CPU gets something even if the switch fails...
Again, please make sure you know what you're doing before attempting this.... no responsibility for any damage to charger.
Sep 04, 2004, 10:24 PM
Senior Member
zagisrule!'s Avatar
I think that they were PIC's of some sort...saw pictures of one in a review. Too small a picture to make out numbers, but the M logo of Microchip is easy to recognize.

Sep 04, 2004, 10:34 PM
Registered Taranis User
Miami Mike's Avatar
Originally Posted by simingx
If it's an EPROM, you can do this:
If they were EPROMs it would be a piece of cake. Someone could read the data and combine it into a chip with twice the capacity, and then do something like you're proposing. The code could even be disassembled and modified if someone had the talent, inclination, and ethical disposition. However, the PDF files from the AstroFlight website say that the chargers use "a proprietary 8 bit microprocessor', which undoubtedly means a microcontroller such as the PIC, with the copy protection feature implimented.
Sep 04, 2004, 11:54 PM
Registered User
like i said, i'm just looking for a switch that'll allow me to switch between the two chips. if i blow it up, then i blow it up. what's the deal wth the different layers of a rotary switch and the different positions/poles. if i figure this out i'll be much happier. thanx in advance. here's the model number from the chip: PIC16C770/P
Last edited by nuttcase21; Sep 04, 2004 at 11:56 PM.

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