A Transcutaneous Electrical Nerve Stimulation (TENS) device is, put bluntly, a machine for giving electric shocks. The author was prescribed such a device on loan by his orthopaedic specialist. The unit has a large number of programmes, of which he used only one. Measuring the signals at the output of the device in this mode revealed damped oscillations at a frequency of approximately 2.5 kHz, with a repetition rate of approximately 100 Hz.
How hard can it be to make such a device ourselves? The simple circuit uses a CMOS 555 timer to produce a brief pulse which feeds a 1:10 miniature transformer. Together with a 4.7 nF capacitor the transformer makes a parallel resonant circuit: the resonance leads to a considerable increase in the output voltage. The pulse width can be adjusted using a potentiometer, here shown combined with the on-off switch. Wider pulses produce higher output voltages. Since a peak voltage of up to 200 V can be produced, the transformer must have adequate insulation: Conrad Electronics type 516260-62 is suitable. A low-cost phono socket at the output gives reliable connection to the electrode cable.
The adhesive electrodes shown in the photograph (disposable and permanent types are available) can be obtained from pharmacies and medical suppliers. They generally have connectors compatible with 2 mm banana plugs, and so it is possible to make up the necessary cable yourself. To treat responsive parts of the body, such as the arm, the potentiometer need not be turned up far to obtain the necessary sensation. Less sensitive parts, such as the knee or foot, need a rather higher voltage and hence a correspondingly higher potentiometer setting.
Author: Klaus Rohwer – Copyright: Elektor Electronics Magazine
Link:http://www.extremecircuits.net/2010/06/transcutaneous-electrical-nerve_03.html
This device is used as a reminder to take medicine every day. This device actually contains a crystal watch and a 4001 quad 2-input NOR gate with two of the gates (IC1a & IC1b) wired as an RS flipflop. The watch is set to “tablet time”, usually mornings, when an alarm is activated with a high signal fed via diode D1 which sets the RS flipflop and enables the oscillator comprising gates IC1c & IC1d. This drives the LED with a 10% duty cycle. The 10nF capacitor resets the watch alarm when positive voltage appears on pin 3 of IC1. The circuit consumes only 50µA with a 3V battery.
Author: Rasim Kucalovic
Source:http://www.extremecircuits.net/2010/05/tablet-reminder-uses-watch-module.html
This electronic game pits a human player against the ‘machine’. The opponents use a common ‘game token’ and take turns moving along a path by one, two or three steps, and the winner is the first one to reach the goal exactly. Incredibly enough, this simple version of the ‘123’ game can be built without a microcontroller, and it’s almost impossible to beat. The electronics for this is built using only diode logic (Figure 1).
The ‘ input inter face’ consists essentially of 30 miniature sockets to which a probe tip can be connected to mark the position of the ‘game token’. To make the game more compact, the sockets are arranged in a grid so the route along the sockets follows a serpentine path (Figure 2). The starting position is at the bottom right, and the goal is in the middle of the playing area. The electronics becomes the ‘active player’ when the button is pressed…….
This is how the LED display works:
The player touches the right-hand contact with R4 (only LED D3 lights up), the left-hand contact with R3 (LEDs D1 and D2 light up), or the middle contact with diodes D4 and D5 (all three LEDs light up). The two diodes prevent all three LEDs from lighting up if the player touches the left-hand or right-hand contact. The key to all this lies in the assignment of the 30 sockets to the three types of logic, which means the three types of ideal next move.
Working backward from the goal, no further move is possible when the goal is reached. For this reason, the last socket is not connected to anything. At the socket just before the goal, the ‘computer’ naturally wants to be exactly one step in front. Consequently, this socket is connected to R4. At the second socket before the goal, the electronics wants to move by two steps. This socket is thus connected to R3……
Source: http://www.extremecircuits.net/2010/05/123-game-all-mcu-free.html
or 
