This is a unregulated supply for low power circuits. You may be able to regulate the outputs with zeners or small regulators like 78L05.
The transformer can be hand wound in a mini ferrite pot core. you can use 2N2222 or any other fast transistor. The transformer should have 1KV isolation. The dot polarity of TR1 should be properly observed, else it may fail to oscillate or give output.
Simple WorkBench Dual Power Supply – del20033
Diode should be fast recovery type, for less than 100mA use 1N4148. transformer, pri-20-20, sec-60-60, a SWG-AWG to suit the current you
design for, any fast switching transistor would work, no regulation, use regulators like 78L12 if you want, circuit like multivibrator used for flashing LED lights.
The Source file in CadSoft EAGLE format is here del00010.zip
U1 7555 is a CMOS version of 555. The 555 here is in Astable Oscillator mode, C1 and C4 are decoupling capacitors 0.1uF value, ceramic disc.
Mixed and Interface Circuits
The output is around 100kHz, If C3 is plastic or mica the frequency output will be stable with temperature. It is better to use a crystal oscillator.
The 555 output is fed to clock input of 4040, the output of 555 will be a square wave, on every high to low transition (falling edge or negative transition) the counter increments by one and the output is 12 bit binary.
Read more at my Digital Timers, Counters and Clocks
If input frequency is F the final output at Q12 is F/4096. The period T = 1/F.
If you make the 555 run at 1Hz, C3 around 7uF, Then this circuit becomes a long duration timer, the Q12 period will be 4096 seconds or 68 minutes.
This is the Analog front end of the 80C39 Process Controller. The analog input is protected by a Zener barrier, low leakage. You could use clamping diodes too.
The non-inverting low-offset amp offers high input impedance. After further amplification it reaches the VCO LM331. The pulse train from the VCO reaches the uC port and is gated and measured by the MCS48 firmware. The voltage is deduced from the Frequency or Pulse width.
You can get a resolution near to a 8-10 bit A/D converter. It does not work for negative voltages. It is a low cost Voltmeter or Process Display solution.
80C39 and MCS48 based Process Controller is the main circuit that has the LED 7 segment display for output and push keys for input.
This shows how to OR gate two 555, when one 555 cycles at a low frequency a valve turns on an off, the second 555 stretches the ON duration of the pulse with a diode OR gate.
Digital Timers Counters and Clocks
The OR output uses sample and hold to get the stable analog data from a sensor after the actuator has gone OFF, this ensures correct reading.
555 is a fundamental Mixed Signal Circuit as it can be made into a VCO using Pin-5. If you see old exar databooks, you can see 555 and PLL and Tone decoders all applications compiled in one base. I feel the Venerable Signetics 555 “Architecture” and Intersil ICL8038 ‘CMOS’ were inspiration behind early communication chip designs, Moving from Bakelite Telephones to Compact Push Button Electronic Phones and more.