Well that one I linked seems very convenient, and I probably wouldn’t need even 1/10th of it current functions. “charging circuit” is generous as it is only a resistor and a diode but a single trace cut disables it. Very interesting Thanks! So the likelihood of two devices with completely different purposes using the same addess range is fairly low, and like my DS1882 audio pot chips, they will usually allow the user to configure 3 bits within the lower nibble of the address. The i2c spec is controlled by NXP: Specification - I2C Bus It means I can now drive multiple displays (up to 8) if I even needed to. And now that you mention it, I see that the board does have places for jumpers (or zero hom SMD parts) to further configure the address. Since its a write only device, I’d think it should be ox3E if anything, but that’s the address needed, so I guess the LCD library I’m using overrides the low bit. Now that I look again, you are right… BUT… the actual address is 0x3F! I’m not sure that makes sense either but because I believe the lowest bit is considered the R/(not)W bit. I’ve never seen a PCF8574 that used address 0x37.Ġx25 is in the address range for the PCF8474s I’ve seen. "charging circuit" is generous as it is only a resistor and a diode but a single trace cut disables it.Īlthough these days for not much more than the cost of an RTC module, you can get a esp8266 module with a powerful processor lots of flash and ram and built in wifi, and then use wifi to sync time using NTP and not even need an RTC at all. If you use a 2032 instead, you should cut a trace on the module to disable the charging circuit. You do need to be careful with most of these low cost RTC modules in the they have a little charging circuit on them for using with a LIR2032. DS3231 modules on ebay (starting at just under $1.50 USD shipped) are cheaper than the price shown on that link you provided to the DS1307. The price is about the same and it is much more accurate.
There is a set of allocated addresses for specific devices.įor an i2c based clock/RTC module would use a DS3231 instead of a DS1307. The i2c spec is controlled by NXP: Specification – I2C Bus Perhaps you meant decimal 37 which is 0x25 ?Ġx25 is in the address range for the PCF8474s I've seen. I've never seen a PCF8574 that used address 0x37. The photo on the aliexpress site shows a PCF8574 chip on the backpack and the backpack supports a configurable address.
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