Key fob only works on battery and not power supply. What's going on here?

Thread Starter

thatsmessedup

Joined Feb 15, 2018
59
Usually every part of that FOB PCB is actually part of the circuit. And the cell body is part of the antenna circuit as well. The result being that almost any addition will alter the performance, and usually not improve it.
looks like you are the correct answer to this post. So, how do they make these things... purely in software?
 

Thread Starter

thatsmessedup

Joined Feb 15, 2018
59
Do you think its a fair assumption that taking out the battery removed quite a bit of metal from inside the loop that is supporting the antennas resonance?
 

MisterBill2

Joined Jan 23, 2018
18,167
Do you think its a fair assumption that taking out the battery removed quite a bit of metal from inside the loop that is supporting the antennas resonance?
Certainly removing the battery reduced the capacitance in most of the circuit. And these devices are designed as a system, rather than as a collection of independent circuit elements. It is even possible that the case enters into the operation.
 

Wolframore

Joined Jan 21, 2019
2,609
yes, I believe its due to the magnetic permeability of the lithium ion cell near the antenna trace. We have the reverse of this issue with nearfield antennas for RFID… it is possible to retune the antenna to work without the battery…

would you mind trying an experiment? Place a dead battery in the compartment with positive terminal insulated from the battery and power it up with the lab supply. Would love to see the output frequency.
 
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