Introduction
The electrical signals generated by living substrates (in slime, plants, fungi, etc) can be tricky to accurately reproduce with conventional electronics due to:
  • low amplitude (sub mV)
  • low frequency (few mHZ)
  • irregular waveform shape
However, it is possible to approximate using some function/arbitrary lifeforms generators and resistor network.


Why generate signals from electronics

The main benefit is consistency. The electrical signals generated by most living creatures vary with stimuli while most electronic circuits are (relatively) stable. For example, if you are trying to optimize/change software you want to minimize the number of variables.

 

Typical configuration

There are hundreds of makes/models of signal generator so the please consult the user manual for your instrumentation. Unfortunately, in most cases it isn’t possible to simply ‘dial up’ the desired signal as outside the normal operating range of the instrument.

 

Reducing signal amplitude

The most common problem is reducing the amplitude of the output signal to match living substrate. This can be achieved by using a resistor network called ‘Voltage Divider’ see below:

The ratio of the two resistors R1 and R2 sets how much the signal from the signal generator is reduced (attenuated).

If R1 is 10 kOhm and R2 is 1 kOhm the output is one tenths. With 10mV input 1mV output 

If R1 is 100 kOhm and R2 is 1 kOhm the output is one hundredth. With 10mV input 0.1mV output 

 

Electrical noise

Most signal generators are power from the mains electric via adapter (some have battery option). PhyLink is connected to your computer/device which may also be connected to mains electric via another adapter. As PhyLink needs to sensitive to record bio-electrical signals it also detects electric noise generated by either adapter and/or computer/device.

The easiest fix is connect the ground/negative of Arduino board to the ‘negative’ of BOTH the differential input and signal generator, see circuit diagram below:

 

The green wire can be plugged into the Arduino’s DC power socket (see photo below)

and then  clipped onto the (negative) connection between PhyLink and signal generator.

 

Reducing signal frequency

The fundamental frequency of oscillation can be reduced to mHz range on more advanced signal generators. Please check the waveform shape on low frequency as the output waveform may be distorted on some signal generators.

 

Waveform shape

The easiest approximation to bio-electrical signals is sine/sinusoidal waveform shape. If your signal generator has the capability you can periodically add higher amplitude spikes.

 

Suppliers of signal generators

There are numerous manufacturers/distributes of different makes/models of signal generators. The more sophisticated versions are sometimes called function/arbitrary lifeforms generators.

In the example above we used FeelTech FY2300 (6MHz) see here.

Martin Lorton has some useful video guides to instrumentation available here.