Wiring schema blogs

This is a really simple sound effect generator based single sound generator chip UM3561. The UM3561 will generate four kinds of sound effects. The basic operation is that the UM3561 will generate the sound signal, then the signal delivered to 2N3706 (as speaker driver) to be amplified so you can hear the sound from a speaker.

Each switch position will generate the follofing sound effect:

• position 1 –> Police Siren
• position 2 –> Fire Engine Siren
• position 3 –> Ambulance Siren
• position 4 –> Machine Gun

Download the UM3561 datasheet for sound effect generator circuit reference:
» Download Link

The circuit in this figure is protecting the circuit and the system with power supplies that may exceed safe limits. One example is small consumer products that use external ac adapters; its easy to mistakenly plug in the wrong adapter. Another example is a portable system that uses a rechargeable battery pack. If the battery pack is absent or fails to open during recharging, a high-compliance charger can deliver excessive voltages to the system.

The circuit works using LM4041 adjustable shunt-voltage regulator as a voltage detector. When it operates as a reference, the LM4041 develops a voltage across its positive and negative terminals. This signal forces the voltage across R₁ to equal 1.24V. In this circuit, however, R₃ prevents this servo action. With R₃ in the circuit, V_G is near ground when the voltage across R₁ is less than 1.24V, and V_G is approximately 1V below the positive rail when the voltage across R₁ is greater than 1.24V. You can, therefore, set a threshold voltage by selecting appropriate values of R₁ and R₂. When the supply voltage exceeds the threshold, V_G goes high, thereby turning off Q₁ and removing power from the load. Select R₁ and R₂ according to:

It where V_SHUTOFF is the supply voltage that causes shutoff. With the values shown, the circuit removes power from the load when the supply voltage reaches approximately 6V. R4 provides hysteresis to prevent chattering when the supply voltage is near the shutoff value. IC₁ can accommodate shutoff voltages as high as 10V; clamping IC₁s supply voltage with another inexpensive shunt reference or zener diode (across the positive and negative terminals) allows higher maximum shutoff voltages. Maximum supply voltage with the components is approximately 50V.

The transmitter schematics.

The principle works of the fire stick is the heart of the Fire-Stick is the Holtek HT-12A encoder IC. This handy little encoder was specifically designed for infrared transmission media, and internally generates the 38 KHz carrier frequency for each data transmission.

The data pins of the HT-12A act as both data input pins & transmit enable inputs. Unlike most ordinary encoder ICs with separate transmit enable pins, and data input pins, the HT-12A uses the data input pins to take care of both input functions.

By pulling one of the data pins to ground, the transmission cycle is started. As with most encoders, a pre-determined sequence of events takes place during each separate transmission cycle. The HT-12A however, has a few internal extras that make it pretty flexible. Notice from the flow chart below that the logic state of the L/MB pin is checked prior to finishing the transmission cycle and returning to standby mode.

To L/MB or not to L/MB:

The L/MB pin serves as the Latch/Momentary selection pin, and determines whether the HT-12A will end each transmission cycle by sending the exact logic state present on each data pin, or end the transmission cycle by sending logic "1" 7 times as the data. If L/MB is left floating, (not connected), the transmission will send only the actual logic values present on each of the HT-12A data input pins. This logic value will be latched onto the output pins of the HT-12D decoder IC until you send another transmission with different data.

The HT-12D decoder IC used on the Fire-Stick receiver normally operates in latched mode. Without the added feature of the L/MB function of the HT-12A encoder IC, the receiver would normally operate in latched mode. Operation of the transmitter causes corresponding data pins of the HT-12D decoder IC to latch at logic 0, or logic 1, depending on the actual logic values present on the HT-12A data input pins, and the state of the L/MB pin.

Using the L/MB option of the HT-12A to select momentary operation of the HT-12D will allow the receiver output pins to be momentarily pulsed low, and then return to logic 1 once the transmission ends, and you release the HT-12A data input pin from ground.

The logic state of all address pins on both the encoder & decoder ICs must be 100% identical or no change will be seen on the decoder output pins. The address pins allow for a certain degree of security, and are beneficial if a similar transmitter will be operated within range of your receiver. This simple method also provides an efficient means of controlling multiple receivers in close proximity to one another with a single transmitter.

With different addresses on multiple receivers you need only adjust the address of the transmitter to match that of each receiver to gain control of that receiver. With 8 address pins, A0 - A7, a total of 256 possible address combinations are possible. This means you can control up to 256 separate receivers with a single transmitter, or have up to 256 possible security addresses for a transmitter/receiver combination.