The equipment

ExpEYES-17 is interfaced and powered by the USB port of the computer, and it is programmable in Python. It can function as a low frequency oscilloscope, function generator, programmable voltage source, frequency counter and data logger. For connecting external signals, it has two spring loaded terminals blocks, one for output signals and another for inputs, as shown in figure 1.1↓. The software can monitor and control the voltages at these terminals. In order to measure other parameters (like temperature, pressure etc.), we need to convert them in to electrical signals by using appropriate sensor elements. The accuracy of the voltage measurements is decided by the stability of the 3.3V reference used, it is 50ppm per degree celcius. The gain and offset errors are eliminated by initial calibration, using a 16bit ADC. Even though our primary objective is to do experiments, you are advised to read through the brief description of the equipment given below. The device can be also used as a test equipment for electrical and electronics engineering experiments.

IMPORTANT :

The external voltages connected to ExpEYES17 must be within the allowed limits. Inputs A1 and A2 must be within ±16 volts range and Inputs IN1 and IN2 must be in 0 to 3.3V range. Exceeding these limits may result in damage to the equipment. To measure higher voltages, scale them down using resistive potential divider networks.

_images/eyes17-panel.jpg

Figure 1.1 The ExpEYES17 top panel showing the external connections.

External connections

The functions of the external connections briefly explained below. All the black coulored terminals are at ground potential, all other voltages are measured with respect to it.

Outputs:

Constant Current Source (CCS) :

The constant current source can be switched ON and OFF under software control. The nominal value is 1.1 mA but may vary from unit to unit, due to component tolerances. To measure the exact value, connect an ammeter from CCS to GND. Another method is to connect a known resistance (~1k) and measure the voltage drop across it. The load resistor should be less than 3k for this current source.

Programmable Voltage (PV1) :

Can be set, from software, to any value in the -5V to +5V range. The resolution is 12 bits, implies a minimum voltage step of around 2.5 millivolts.

Programmable Voltage (PV2) :

Can be set, from software, to any value in the -3.3V to +3.3V range. The resolution is 12 bits.

Square Wave SQ1:

Output swings from 0 to 5 volts and frequency can be varied 4Hz to 100kHz. All intermediate values of frequency are not possible. The duty cycle of the output is programmable. Setting frequency to 0Hz will make the output HIGH and setting it to  − 1 will make it LOW, in both cases the wave generation is disabled. SQR1 output has a 100~\Omega series resistor inside so that it can drive LEDs directly.

Square Wave SQ2:

Output swings from 0 to 5 volts and frequency can be varied 4Hz to 100kHz. All intermediate values of frequency are not possible. The duty cycle of the output is programmable. SQR2 is not available when WG is active.

Digital Output (OD1) :

The voltage at OD1 can be set to 0 or 5 volts, using software.

Sine/Triangular Wave WG:

Frequency can be varied from 5Hz to 5kHz. The peak value of the amplitude can be set to 3 volts, 1.0 volt or 80 mV. Shape of the output waveform is programmable. Using the GUI sine or triangular can be selected. WG bar is inverted WG.

Inputs:

Capacitance meter IN1:

Capacitance connected between IN1 and Ground can be measured. It works better for lower capacitance values, upto 10 nanoFarads, results may not be very accurate beyond that.

Frequency Counter IN2:

Capable of measuring frequencies upto several MHz.

Resistive Sensor Input (SEN):

This is mainly meant for sensors like Light Dependent Resistor, Thermistor, Photo-transistor etc. SEN is internally connected to 3.3 volts through a 5.1kΩ resistor.

\pm16\ V Analog Inputs, A1 & A2:

Can measure voltage within the ±16 volts range. The input voltage range can be selected from .5V to 16V fullscale. Voltage at these terminals can be displayed as a function of time, giving the functionality of a low frequency oscilloscope. The maximum sampling rate is 1 Msps /channel. Both have an input impedance of 1MΩ .

\pm3.3\ V Analog Input A3:

Can measure voltage within the ±3.3 volts range. The input can be amplified by connecting a resistor from Rg to Ground, gain =1 + (Rg)/(10000). This enables displaying very small amplitude signals. The input impedance of A3 is 10MΩ.

Microphone input MIC:

A condenser microphone can be connected to this terminal and the output can be captured.

I2C Sensor Interface:

The four connections (+5V, Ground, SCL and SDA) of the 8 terminal berg strip supports I2C sensors. The software is capable of recognizing a large number of commercially available I2C sensors.

\pm\ 6\ V/10\ mA Power supply:

The VR+ and VR- are regulated power outputs. They can supply very little current, but good enough to power an Op-Amp.

1.2.2 Accessory Set

Some accessories are provided with expEYES.

  • Pieces of wires, with pin and with crocodile clip.
  • Condenser microphone with leads.
  • Inductor Coil (2) : 44SWG wire on 1cm dia bobbin. Around 3000 Turns (some may have more turns). These coils can be used for studying inductance, electromagnetic induction etc.
  • Piezo Electric Discs (2) : Resonant frequency is around 3500 Hz. Can be energized by WG output or SQR1. Discs are enclosed in a plastic shell that forms a cavity, that enhances the amplitude of sound produced.
  • DC Motor : Should be powered by a DC voltage less than 3 volts.
  • Permanent Magnets : (a) 10mm dia & length (b) 5 mm dia & 10 mm length (c) Button size magnets(2)
  • 5mm LEDS : RED, BLUE, GREEN, WHITE
  • Capacitors : 100pF, 0.1uF , 1 uF & 22uF
  • Inductor : 10 mH / 20Ω,
  • Resistors : 560Ω, 1kΩ, 2.2kΩ , 10kΩ , 51kΩ and 100 kΩ
  • LDR
  • Two silicon diodes (1N4148) and one 3.3 volts zener diode
  • NPN Transistor( 2N2222)