Rather than use DC leakage with a strong CM line AC signal present for touch sensing, this EMI problem may be solved better ways.

It seems your SNR <1 (unless poorly biased, filtered)

Put a shunt R of 1M to earth gnd and also a >10nF across Vbe with a line f pulse stretcher cap across Vce to RC>20 ms....Otherwise.... plan B

————

Normally for touch switches a frequency in the x or xx kHz range is sensed by amplitude across the contacts. But here there is only 1 contact (bar) and the other is internal Earth-bonded ground.

So how to detect injected common mode (CM) signal at some frequency on an “earthed bar”?

Assumptions

The impedance of the bar is unknown but assumed to provide a safe contact in case of a lightning strike or wiring fault. The human’s impedance for a finger using the HBM (model) is 100 pF + ? R but also the parasitic insulation R (wide range !) and RF characteristic Impedance (377 ohms ) in series with a high C , low R body plasma to a distant earth ground.

I assume you know how to compute impedance for L or C (f).

Thought experiment

Which would work better?

1. Use an Inductor to bar instead of a wire of impedance X(f) and detect 50V E-field (seen) on 10Meg probe) but now attenuated to xx ? mV line f by ground shunt series L and detect 50,60 Hz low level above e-gnd.
2. Inject a 100kHz to 500kHz signal into “bar” and suppress with finger capacitance and detect drop in carrier with a BPF and Detector/comparator,
3. Assume one-shot timer comparator in both to select dim or toggle power.

Rather than use DC leakage with a strong CM line AC signal present for touch sensing, this EMI problem may be solved better ways.

It seems your SNR <1 (unless poorly biased, filtered)

Put a shunt R of 1M to earth gnd (across Vbe) and also a >10nF across Vbe with a line f pulse stretcher cap across Vce or across Rc so that RC>20 ms..This will also suppress ESD if low ESR plastic by 100pF/10nF ..Otherwise.... plan B.

————

Normally for touch switches a frequency in the x or xx kHz range is sensed by amplitude across the contacts. But here there is only 1 contact (bar) and the other is internal Earth-bonded ground.

So how to detect injected common mode (CM) signal at some frequency on an “earthed bar”?

Assumptions

The impedance of the bar is unknown but assumed to provide a safe contact in case of a lightning strike or wiring fault. The human’s impedance for a finger using the HBM (model) is 100 pF + ? R but also the parasitic insulation R (wide range !) and RF characteristic Impedance (377 ohms ) in series with a high C , low R body plasma to a distant earth ground.

I assume you know how to compute impedance for L or C (f).

Thought experiment

Which would work better?

1. Use an Inductor to bar instead of a wire of impedance X(f) and detect 50V E-field (seen) on 10Meg probe) but now attenuated to xx ? mV line f by ground shunt series L and detect 50,60 Hz low level above e-gnd.
2. Inject a 100kHz to 500kHz signal into “bar” and suppress with finger capacitance and detect drop in carrier with a BPF and Detector/comparator,
3. Assume one-shot timer comparator in both to select dim or toggle power.

Rather than use DC leakage with a strong CM line AC signal present for touch sensing, this EMI problem may be solved batter ways.

Normally for touch switches a frequency in the x or xx kHz range is sensed by amplitude across the contacts. But here there is only 1 contact (bar) and the other is internal Earth-bonded ground.

So how to detect injected common mode (CM) signal at some frequency on an “earthed bar”?

Assumptions

The impedance of the bar is unknown but assumed to provide a safe contact in case of a lightning strike or wiring fault. The human’s impedance for a finger using the HBM (model) is 100 pF + ? R but also the parasitic insulation R (wide range !) and RF characteristic Impedance (377 ohms ) in series with a high C , low R body plasma to a distant earth ground.

I assume you know how to compute impedance for L or C (f).

Thought experiment

Which would work better?

1. Use an Inductor to bar instead of a wire of impedance X(f) and detect 50V E-field (seen) on 10Meg probe) but now attenuated to xx ? mV line f by ground shunt series L and detect 50,60 Hz low level above e-gnd.
2. Inject a 100kHz to 500kHz signal into “bar” and suppress with finger capacitance and detect drop in carrier with a BPF and Detector/comparator,
3. Assume one-shot timer comparator in both to select dim or toggle power.

Rather than use DC leakage with a strong CM line AC signal present for touch sensing, this EMI problem may be solved better ways.

It seems your SNR <1 (unless poorly biased, filtered)

Put a shunt R of 1M to earth gnd and also a >10nF across Vbe with a line f pulse stretcher cap across Vce to RC>20 ms....Otherwise.... plan B

————

Normally for touch switches a frequency in the x or xx kHz range is sensed by amplitude across the contacts. But here there is only 1 contact (bar) and the other is internal Earth-bonded ground.

So how to detect injected common mode (CM) signal at some frequency on an “earthed bar”?

Assumptions

The impedance of the bar is unknown but assumed to provide a safe contact in case of a lightning strike or wiring fault. The human’s impedance for a finger using the HBM (model) is 100 pF + ? R but also the parasitic insulation R (wide range !) and RF characteristic Impedance (377 ohms ) in series with a high C , low R body plasma to a distant earth ground.

I assume you know how to compute impedance for L or C (f).

Thought experiment

Which would work better?

1. Use an Inductor to bar instead of a wire of impedance X(f) and detect 50V E-field (seen) on 10Meg probe) but now attenuated to xx ? mV line f by ground shunt series L and detect 50,60 Hz low level above e-gnd.
2. Inject a 100kHz to 500kHz signal into “bar” and suppress with finger capacitance and detect drop in carrier with a BPF and Detector/comparator,
3. Assume one-shot timer comparator in both to select dim or toggle power.