LM IC 1. This IC and circuit is now a piece of history. I had one of these circuits running on a PCB for years, the circuit finally failed. My attempts to repair the circuit were unsuccessful. It appears that the IC finally failed.
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The added High frequency operation requires addition of two external 75X series resistor for the LED keeps current peaks within resistors, typically of the same value. One, of course, shunts safe limits for the diode and IC. Also, in operation above a the high internal timing resistors. If only this one were used, 3V supply, the electrolytic capacitor sees momentary volt- the capacitor charging current would have to pass through age reversals.
It should be rated for periodic reversals of the two X resistors internally connected between pin 5 1. Oscillation at a slower rate and A continuously appearing indicator light can also be pow- lower duty cycle than desired would occur, and oscillation ered from a single 1. Duty cycle might cease altogether before the battery was fully dis- and frequency of the current pulses to the LED are in- charged.
The second 68X resistor shunting the two X creased until the average energy supplied provides suffi- resistors eliminates these problems. At frequencies above 2 kHz, even the fastest The circuit in Figure 5 is a relaxation type oscillator flashing movement of the light source or the observers head will not 2 LEDs sequentially.
With a 12 VDC supply, repetition rate is produce significant flicker. C2, the timing and storage capacitor, alternately Since this indicator powering circuit uses the smallest ca- charges through the upper LED and is discharged through pacitor that will reliably provide full output voltage, its oper- the other by the ICs power transistor, Q3.
A drain is about 12 mA. Continuous 1. Alternating Flasher 4 Indication or monitoring of a high voltage power supply at a The timing capacitor is charged through the dropping resis- remote location can be done much more safely than with tor and the two X collector loads between pins 2 and 5 neon lamps.
If the dropping resistor 43k as in Figure 6 is of the IC. When capacitor voltage reaches about 5V, there located at the source end, all other voltages on the line, the is enough voltage across the 1k resistor to pin 8 to turn on IC, and the LED will be limited to less than 7V, above Q1, and hence trigger on the whole IC to discharge the ca- ground.
A chart outlining operation of the circuit of Figure 6 with a large reflector. In a dark room, the flashes were al- at various voltages appears on the LM data sheet.
Also most fast enough to stop a persons motion. As a toy, the shown are circuits for adjusting the flash rate, flashing 4 fast setting can mimic the strobes at rock concerts or the LEDs in parallel, and details for building a blinking locator flicker of old-time movies. Figure 8 below shows a higher power application such as Incandescent bulbs can also be flashed, as already illustrat- would use an automotive storage battery for power.
It pro- ed in Figure 1. However, most such bulbs draw more than vides about a 1 Hz flash rate and powers a lamp drawing a the mA that the LM can switch. The two following nominal mA. In each circuit, an NPN transistor is used, so the external wires and thus may be hooked up in either of the power transistors base drive is obtained from the common two ways shown below in Figure 9.
Further, no circuit failure or ground pin of the flasher IC. The In the circuit of Figure 8 , the mF capacitor performs a rate control is so wide range that it adjusts from no flashes number of other functions.
It makes the LM immune to at all to continuously on. Chosen for rapid response, the supply spikes, and provides the means of limiting the ICs miniature lamp can be flashed several times a second. Quick attached to pin 8 of the IC causes it to turn fully on at 7V or checks for shorts and opens in transformers and motors less on pin 5. Then the LM discharges the timing ca- can therefore be made. The capacitor discharge current comes out of pin shops can often suffer damage from spills or water seepage 4 of the IC, turning on the NSD U01 transistor.
It is the large ruining lumber, chemicals, fertilizer, bags of dry concrete, size of the timing capacitor that allows it to store all the etc. The circuit of Figure 11 is safe on potentially damp needed energy for turning on the power transistor. This in floors since there is no connection to the power line.
Fur- turn permits the whole flasher circuit to operate as a 2 wire ther, its standby battery drain of mA yields a battery life device. LED flash rate can be shelf life. With a 3V supply, yellow and green LEDs may be off, and its collector load 6.
A 6V incandescent emergency lantern can be hold pin 8 of the LM above 0. When the sense electrodes pass about 0. This is a more reliable, moisture, Qa starts turning on, and since Qb is already par- longer lived system than a lantern with a second thermal tially biased on, positive feedback now occurs. Qa and Qb flasher bulb. The NSL Current Regulated LED makes are now an astable multivibrator which starts at about 1 Hz possible flashing many LEDs in parallel or with high volt- and oscillates faster as more leakage passes across the ages without series resistors.
Very economical continuity checkers, tone generators, and The pulse waveform at the collector of Qa varies the timing alarms may be made from the LM No matching trans- current through the 3. LM output can drive many standard permanent magnet The sensor should be part of the base of the box the alarm transistor radio loudspeakers directly.
The 1. Two strips of lasting than the conventional 9V battery. By probing 2 values in quick succession, should be coated with warm wax so that moisture on the small differences such as between a short and 5X can be floor, not that absorbed by the board, will be detected. The detected by differences in tone. A novel use of this circuit is found in setting the timing of certain types of motorcyles.
This is due to the difference in Minimum cost, simplicity, and very low power drain are the tone that can be heard from the tester depending whether aims of the Morse Code set of Figure One oscillator there is a short or not across the low resistance primary of simultaneously drives speakers at both sending and receiv- the cycles ignition coil.
Morse Code Set 8 ing ends. Calculations and actual use tests indicate life of a slide in and out like a piston. The box was stiffened with thin single alkaline penlight cell to be 3 months to over a year layers of pressed wood, etc.
Minimum volume with the pis- depending on usage. Buzzer type sets use two or more ton in was about 10 in. Speaker, circuit, battery, and all batteries with much shorter life.
The three in. ID to bleed air in and out as the piston was moved while wire system and parallel telegraph keys allow beginners and not affecting resonant frequency. Acoustically, both speakers are op- tune after a few tries. Each of collector and the speaker, decouples voltages generated the two speaker enclosures has holes added to augment by the resonating speaker system from the low impedance this resonance.
For each different type or brand of speaker switching action of Q3. The mF feedback capacitor and size of box, hole and capacitor sizes will have to be would normally set a low or even sub-audio oscillation fre- determined by experiment for the most stable resonant tone quency. Therefore, the major positive feedback voltage to over the expected battery voltage variation.
Therefore the LM will continue to circuit in Figure It is optimized to oscillate at any acous- drive the speaker at the resonance with the highest com- tic load frequency of resonance!
With just a speaker, oscilla- bined amplitude and frequency. If the It can be seen already that the LM, having direct speaker is in an enclosure with a higher resonant frequency speaker drive and resonance following capability, can do. Two final sound effect type of circuits An educational audio demonstration device, or simply an are illustrated in Figure A roughly cu- bical box of about 64 in.
Electronic Trombone 9 The siren of Figure 14a produces a rapidly rising wail upon the pushbutton increases current in the 2. If it is desirable to have the tone stop sometime The whooper of Figure 14b sounds somewhat like the after the button is released, an 18k resistor may be placed electronic sirens used on city police cars, ambulances, and between pins 8 and 6 of the IC. The sound is then much like airport crash wagons.
The rapid modulation makes the that of a motor driven siren. In this circuit, the oscillation must not be influenced by The tone generator is the same as in the previous siren. The 1 mF capacitor and X resistor Instead of a pushbutton, a rapidly rising and falling modulat- determine a pulse to the speaker that is wider than that for ing voltage is generated by a second LM and its asso- flashing LEDs, but much narrower than is used in the tuned ciated mF capacitor.
The 2N transistor is used as a systems of Figures 12 and The repetition rate of speak- low voltage germanium diode. This transistor along with er pulses is determined by the 2.
LM3909N - LM3909 LED Flasher/Oscillator Datasheet