RSSI and AoA for tiny consumer micro-locator ?

An interesting project! Nice concept for both individual item location & home automation.


The battery size/type is confused though - you first list a lithium cell. CR1225 which is 12mm diameter by 2.5mm thick.

I see "V355" in a drawing, but the data sheet is for a 335 / SR512SW.


That is a problem.. You do not appear to have allowed for the transmit current, ~9 to 14mA (data sheet section 5.5).

The SR512SW is not really intended for high loads; the "high current" pulse test in the datasheet uses a 2K load, so around 0.6mA (compared to around 9uA for normal discharge).

That 9+ mA is likely to kill the battery and reset the IC, either instantly or quite early on, compared to the expected life if the current was low.

It would need a fairly large capacitor to buffer the IC current, at least, if it could work at all with that cell.

That's a "low drain" cell type, according to Renata - they categorise cell types as low or high drain, plus special high pulse types (not listed in that data); see here:

Thank you! Yeah I had that confused from a previous project. So then I would have to go slightly wider, slightly thicker or both but either of these should work right?

Those are still both in the "Low drain" class rather than high drain; the 361 or 376 are fairly small, in the high drain class?
- But, the data does not give any info on peak current capabilities for any of those.


I think you need to contact Renata technical support to find out from them what cells can support the peak current the transmitter needs, without compromising the battery life too much.

Thank you! I'll give them A call. I think low friends is what I'm looking for since I want the battery to last for multiply years but like you pointed out there are those spikes that it needs to be able to handle as well.

A common technique for long life batteries is to add a super capacitor across it, with the super capacitor providing the high current pulses which the long life batteries are unable to supply.

However, I suspect the tiny size requirement might preclude that?.

Consider modeling, simulation, the combo of super cap and battery, as the
super cap, for small valued caps, has fairly high Z and so its effectiveness
at handling pulses may not be a good solution. Depends on your tolerance
for magnitude of transient V drop. Looking at a 2032 coin cell itsZ ~ 20 ohms,
the smallest supercap 60 ohms. It helps but not all that great.


Regards, Dana.