Sometimes I need to disconnect my ESD wrist strap, but forget to reconnect it again. Apart from improving my discipline to work more structured and more carefully, I wondered if there was any device/circuit that could warn me for not having reconnected the ESD wrist strap.
Searching on internet, I found an ESD wrist strap with build in ground alarm
How does such a device work, how does it detect a disconnection of the wrist wrap?
I couldn't find any schematic on internet, so thought of a schematic how I think it may have been implemented.
A (modulated?) current source causes a defined voltage drop across R_device when SW1 is open.
As soon as the ESD wrist wrap is connected (pictured by SW1), the series resistance of R_connection_wire plus R_wrist_wrap plus R_human_body plus R_shoes/floor will be in parallel with R_device, which will lower the defined voltage drop.
With a multimeter, I measured the resistance of my own wrist wrap (bad measurement, but not relevant anyway) and the resistance of the connection wire to the wrist wrap. I made assumptions w.r.t. to the resistance of the human body and other resistances in the path (shoes, floor).
Next to the question:
How does the ESD wrist strap with build in ground alarm detect a disconnection of the wrist wrap?
I'd like also to ask:
Do you have other ideas/suggestions to detect a disconnection of the wrist wrap?