TREE

This circuit shows how to build a super-sensitive, mini-powered FM transmitter consisting of a RF (radio Frequency) oscillator section interfaced with a high sensitivity, wide pass-band audio amplifier and capacitance mike with a built-in FET (Field Effect Transistor) that modulates the base of the RF oscillator transistor. Transistor Q1 forms a relatively stable RF oscillator whose frequency and is determined by the value of coil L1 and turning capacitor C4. Part List : R1_______15K R2_______3K9 R3_______220R R4,R5____1K R6,R9____10K R7_______390K C1,C6____0.01uF C2_______4.7pF C3_______0.1uF C4_______6-35pf trimmer cap C5_______2.2uF B1_______3V L1_______Coil winding (see below) Q1,Q2____PN2222 M1_______Special FET bypassed microphone Assemble L1 : Form L1 by tightly wrapping eight turns of #16 bus wire on a #8 wood screw. Produces an eight-turn coil with an inner diameter of approximately 0.135 inches and lenght of about 0.625 inches. Insert in the proper hole and solder as shown.

It is sometimes disturbing to have a AM radio in a countryside and not being able to get the reception clearly. It is simply because of the distance of the radio station and also the strength of the station. The only solution is to attach a powerful antenna to the receiving radio the uniqueness of the antenna lies in its simplicity and cost. The basic knowledge of making an antenna is there in the back end. Generally, the frequency range of amplitude modulation in 560 to 1650 KHz in order to resonate the LC circuit that that is the antenna (2πfL=1/(2πf_c )) 4πf^2 LC=1.Using this formula and using a 30- 450 pF gang condenser the handy inductance built on a 350ft long PVC pipe works quite well. The inductance built around a PVC pipe is basically an air core inductor, the inductance of which is govern by the formula L=(R^2 N^2)/(9R+10l) where L is inductance in μH, R is coil radius in inches, l is coil length in inches and N is number of turns. The calculated inductance in tune with 3...

Long-Interval Pulse Generator Circuit Diagram. A rectangular-wave pulse generator with an extremely long period can be built using only two components: a National Semiconductor LM3710 supervisor IC and a 100-nF capacitor to eliminate noise spikes. This circuit utilises the watchdog and reset timers in the LM3710. The watchdog timer is reset when an edge appears on the WDI input (pin 4). If WDI is continuously held at ground level, there are not any edges and the watchdog times out. After an interval TB, it triggers a reset pulse with a duration TA and is reloaded with its initial value. The cycle then starts all over again. As a result, pulses with a period of TA + TB are present at the RESET output (pin 10).  Long-Interval Pulse Generator Circuit Diagram   Long-Interval Pulse Generator Circuit Diagram As can be seen from the table, periods ranging up to around 30 seconds can be achieved in this manner. The two intervals TA and TB are determined by internal timers in the IC, ...