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This resistor might be anything from 50K to 700K depending on the gain of the transistor used where the 3904 is shown. To optimize the operation, select a resistor where the 100K is shown to set the output voltage at 1/2 the supply voltage (4.5 volts). ![]() The circuit should work with a regular 8 ohm speaker, but the output power may be somewhat less. But you should take care to insure the idle current is around 10 to 20 milliamps with no signal and the output transistors do not get hot under load. Please check the Pic Programmer section of the website for the updated DIY pack for them. The 2 diodes generate a fairly constant bias voltage as the battery drains and reduces crossover distortion. Serial RS232 and serial TTL interface, 9600 baud, 8 data bits, 1 stop bit, no parity, no. A 2N3904 or 2N3906 are probably a little small, but would work at low volume. Most any small transistors can be used, but they should be capable of 100mA or more current. If you need something like this you need to assemble a very simple circuit (Programmer Unit).Hardware:Figure 1 shows the Block diagram of the in-system programmer interface, the programmer can be self powered or target. The transistors shown 2n3053 and 2n2905 are just parts I used for the other circuit above and could be smaller types. This In System Programmer is RS232 (serial port) based but can indirectly be used with USB using USB to RS232 converter. The original circuit in the radio used a 300 ohm resistor where the 2 diodes are shown but I changed the resistor to 2 diodes so the amp would operate on lower voltages with less distortion. When the output moves positive, the charge on the 470uF capacitor aids in turning on the top NPN transistor. In this circuit, the 1K load resistor is tied to the speaker so that as the output moves negative, the voltage on the 1K resistor is reduced, which aids in turning off the top NPN transistor. But it's an improvement over the other circuit above. The output still won't move more than a couple volts using small transistors since the peak current won't be more than 100mA or so into a 25 ohm load. This circuit corrects the problem somewhat and allows a larger voltage swing and probably more output power, but I don't know how much without doing a lot of testing. 2) Press and hold the set up button till the red light on the left hand corner stays on. #AT89C2051 PROGRAMMER USING USB TO SERIAL TTL TV#Thus the output cannot move all the way to the + supply because there wouldn't be any voltage across the 470 resistor and no base current to the NPN transistor. The codes for sony are 0128, 0013, 0002, 0071, 0380, or 0152 1) Make sure the tv is on. This has a disadvantage in that as the output moves positive, the drop across the 470 ohm resistor decreases which reduces the base current to the top NPN transistor. #AT89C2051 PROGRAMMER USING USB TO SERIAL TTL DRIVER#In the circuit above, the load resistor for the driver transistor is tied directly to the + supply. ![]() I copied it from a small 5 transistor radio that uses a 25 ohm speaker. This circuit is similar to the one above but uses positive feedback to get a little more amplitude to the speaker. ![]()
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