Sharring an EEPROM with 2 PICs

[lilimike]

I want to share an EEPROM 24CL16 between 2 PICs.

PIC#1: I have no control of, it reads the EEPROM permanently and update a counter daily until it reach a value of 0.

PIC#2: Is the project I am designing, it will reset the EEPROM to its original value at the press of a button.

I figured I would install a relay and disconnect PIC#1 while I do the reset from PIC#2. Ideally I was looking for an SSR at Digikey that could be driven directly from the PIC but they are either too expensive or input voltage is too low which would require extra components.

I came upon this. will it work?


Mike

 

[Pommie]

As you appear to be implementing a reset function, why not have the second pic hold the first pics reset line low while you access the EEPROM.

Other than that, it's hard to advise without knowing more about the system.

Mike.

 

[Wilksey]

Interesting question,

A SSR is not necessary! Why is the first PIC constantly reading the EEPROM? Will it impact upon it if the EEPROM cannot be read? i.e. whilst the other PIC is reading it?

Your link is for a USB switch, again, probably not suitable.

I presume you are using the SCL and SDA lines to read the EEPROM? well, one way to do this would be to have 2 sets of 2 transistors maybe as a simple switch, where the 2nd pic controls both sets, so switches the first PIC off and switches itself on, and vice versa.

I guess since it is voltage levels this would work?

Wilksey

 

[lilimike]

I am working on a Cat Genie, it has its own PIC which I don't really want to mess with.
This thing has a cartridge to disinfect the cat granules during the wash and it is good for 60 cycles. After this they expect me to throw the cartridge in the garbage and buy a new one for $20. The cartridge is equipped with a 24CL16 chip which keeps the count and it is linked by 4 wires to PIC#1 (ie Power and I2C)
I don't want to play on the PIC#1 circuit but it is a simple job to just bypass the wires to do the reset.

Mike

 

[lilimike]

Interesting question,

Your link is for a USB switch, again, probably not suitable.

Why wouldn't the USB switch work? if it can support 720MHz and its input voltage is 5Volts, I am working at 100 KHz.
Is there something I am not understanding from the datasheet?

Mike

 

[birdman0_o]

Hello from Montreal. Had a good laugh when I saw the cat toilet, is it any good?

 

[Brevor]

If you Google "cat genie cartridge reset" you will see some other solutions. It seems like the easiest solution would be to build a reader/programmer circuit that can read the contents of a new cartridge, and then program that value into the used cartridge.

 

[lilimike]

Hi Mike,
This cat toilet is excellent, I've had this for a few years and I don't have to deal with smelly litter or cleaning, it does its daily cleaning all by itself, I just do a guts cleaning once every 6 months.

Hi Brevor,
I have been using that other solution so far but every time it needs a reset I have to bring the cartridge to the computer, hook it up to serial programmer and reprogram. What i am doing will reset the cartridge by the simple press of a button located on the toilet. Simple enough that my wife can do it.

Mike

 

[Wilksey]

I said probably, not definately not, I dont know how much those chips are, just seems a bit overkill for a dpdt switch, I also dont know how much "optimisation" they have done.

Do you need that much bandwidth or would something like this be suitable for you:
ON Semiconductor NLAS44599: Dual DPDT Analog Switch

If you would rather go for the USB one, then there is no reason if it acts as a simple switch that it wouldn't work, but the only way to try it is get one and see!

Wilksey

 

[lilimike]

Today I went for a tour of the surplus stores and I found a miniature 5V DPDT relay. It pulls just a little too much current to drive directly from the PIC (35mA) so I guess I will just use one NPN transistor to drive it. I guess a relay a transistor a diode and a couple resistors wont make the circuit that much bigger. It's just a personal thing I have to always try to make my circuits as small as possible.

Thanks for your replies.

Mike

 

[LTX71CM]

Why can't you lift the 24CL16's WriteProtect pin and tie it high? Then it can be read but not altered. Problem solved. No?

 

[lilimike]

Not quite...
I need the toilet to sound its alarm after the 60th cycle so this way I know I have to refill the cartridge and then I reset it.
In the cartridge there is 16 oz of disinfectant and I want to make sure it is never empty.

Another thing is, the chip is not accessible (without braking the cartridge and making a mess)

Mike

 

[Mr RB]

(edit)I replied to post #11 but my reply was unnecessary after reading #12.

 

[lilimike]

Mr RB you are probably right.
But one thing I can say, whoever put this idea on the market is a genius, a wash takes 20 to 30 minutes and I can tell by the way the program works they must of spend weeks or months observing and timing everything because 99% of every wash picks up every thing the cat left behind.


EDIT: See it in action here

PS: No I don't work for them but for the price I paid $350, I should have shares in that company.

Mike