Sobriety Tester

With all the holidays upon us, understandably some of us will be drinking alcoholic beverages. This circuit can be used as a guideline how much you have had to drink and how good your reaction time is. This circuit does not tell you whether you are over the legal limit of alcohol in in your blood. This circuit can also be use for fun to test your reaction time. The circuit works as follows. Imagine for the moment that S1 switch is depressed which causes it to be open and S2 switch is closed. On command from someone acting as the tester, the person depressing S1 must remove his/her hand from the switch S1 and with the same hand toggle switch S2 to the open position.. When S1 is released, charging current begins to flow into capacitor C2 through R1 and R2. This current is interrupted, however, as soon as S2 has been opened. C2 will have accumulated a voltage directly proportional to the reaction time, which is the interval between S1's release and the opening of S2. Longer times create higher voltages and cause higher numbered LED's to light. For example, a sober person might react quickly enough to light LED 2 or LED , while someone truly sloshed will light up to LED 10. To run another test, discharge C2 with S3, then press S1 and, finally, close s2 once more. R1 should be adjusted so that a sober person lights one of the low numbered LED's. The supply voltage says 18 volts but 9, 12, or 15 will work fine also.

Form : http://home.maine.rr.com/randylinscott/dec21.htm

Guitar Tuning Aid

The basis of this circuit is the 555 timer operating in the astable mode. The oscillating output can be used as a tuning aid for a guitar. The first string of a guitar ,E, produces a frequency of 82.4 Hz. The frequency of the oscillator is set to twice this value, 164.8 Hz. and then followed by a dived by 2 stage to provide the required frequency. The purpose of the divide by 2 stage is to guarantee that the waveform produced has a duty cycle of 50%. The frequency of oscillation of the circuit is set by the adjustment of R1,R2 and C4. The output of IC2 is fed to the emitter follower Q1 to produce current gain to drive the speaker. C3 acts as a high pass filter to attenuate harmonics and produce a natural sounding note. The circuit is powered by 5 volt dc supply and this voltage must fall within the range of 4.74 to 5.25 volts for IC2 to operate properly.

From : http://home.maine.rr.com/randylinscott/nov21.htm

VOM Light Meter

This circuit detects the amount of light that is shining on the phototransistor Q1. As the light intensity increases at the input of Q1 the voltage output gets amplified by the 741 op amp IC1. You can typically purchase a analog meter movement unit from Radio Shack still and alot of surplus mail order companies.

From : http://home.maine.rr.com/randylinscott/oct21.htm

Hands Off

This circuit is based on the 555 timer. It is used to detect whether someone is touching the tip of resistor R2 or is coming close to it. R2 can be connected to anything metal, for example a small piece of copper or tin foil, etc. When someone's hand comes close to this piece of metal or touches it, it will cause the 555 to trigger on pin 2 which will cause it to output a high on pin 3 and turn on the LED. Not only will it turn on the LED but it will also cause the UJT to oscillate and output an alarm sound through the speaker. The tone of the sound is controlled by the combination values of R4 and C3. The UJT Q1 is a 2N2646 but any small signal UJT will work fine.

From : http://home.maine.rr.com/randylinscott/sep21.htm

Alternate Action Button

I am starting this month with some scans of circuits that I have used years ago that are still useful today. Hopefully the scans are clear enough.
By pressing S1 momentary switch, the 4069 hex inverter will cause the relay to turn on. When S1 is pressed again it will cause the relay to go off. This simple circuit can be used for the bases of many projects. The transistor in the circuit provides enough current to drive the relay.

From : http://home.maine.rr.com/randylinscott/aug21.htm

60 LED Clock

This months project is based on the 4017 chip that we used in a project last month. If you haven't had a chance to review the basics of the 4017 chip you may want to review the info presented in June's project of the month.
As you can see see we have changed the circuit a little. For example, the 4093 NAND gate is now set to exactly 1 second clock pulses. The clock rate is determined by the resistor and capacitor combination on the 4093. If the resistor is 220k ohms and the capacitor is 4.7uf then the output will be 1 second clock pulses. To increase the clock rate you should decrease the value of the resistor or capacitor. To decrease the clock rate you should increase the value of the resistor or capacitor. Please remember to ground all unused legs of the 4093 or noise in the circuit will occur and cause the clock to malfunction. Therefore, ground pins 5,6,8,9,12, and 13. To operate the circuit simply move the switch from STOP to RUN.

From : http://home.maine.rr.com/randylinscott/jul21.htm

Count To Ten With Lights

The circuit presented this month is a basic configuration of the very versatile 4017 IC Chip. In the most common use of the IC, it will turn on 10 separate outputs sequentially. Typically, the circuit is used to turn on a LED for certain time cycle. In the circuit shown the VR can be adjusted so that the clock output of the NAND gate will be 1 second. With this clock at 1 second intervals, the 4017 chip will turn on output # 0 to be high which will light and LED. When clock pulse 2 is received a second later, output #1 will go high which will turn on LED2. This process will continue until all 10 outputs have gone on and then it will start all over again until you turn the power off. When building this circuit you should tie the left over pins of the other NAND gates in the CD4093 to ground. Therefore, pins 5,6,8,9, 12 and 13 should be connected to ground.

From : http://home.maine.rr.com/randylinscott/jun21.htm

Quick Draw

The object of Quick Draw is to test your reaction time against your opponent's. A third person acts as a referee and begins the duel by pressing S1, which lights LED1. Upon seeing LED1 go on, you try to outdraw your opponent by moving S2 from "Holster" position to "Draw" position before your opponent moves S3 from "Holster" to "Draw" position. Who ever gets there first will light the corresponding LED and will automatically prevent the other LED from lighting, clearly indicating a winner.

From : http://home.maine.rr.com/randylinscott/may21.htm