Alan’s Stairstep Generator Using 555 and Op Amps

Again, difficult for me – too many errors building the thing at my age with eyesight and senility! I think good quality kit makes a big diff here though with non exact values for some caps and resistors throwing out timing multiples for even steps etc? – too much noise for clarity in the fine divisions to get a clear stair step. Best I got was uneven and spiky spread at the trigger start:

Weather Station Complete

Packed in a Neo6 GPS, BMP180, DHT11 and OLED screen controlled by a Nano fixed into female headers for easy component swap out and height gain- shame about my engineering skills, works, and finally used that 6 year old project box..:

Nano code:

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Aluuminium Box £5?

Total : £25

16Mhz Crystal Oscillator Actually at 16Mhz!

Again, due to the breadboard affects on crystals, my  circuit was slightly different than Alan’s by the lucky trial and error of my incorrect cap value components removal – including a floating caramic cap at the base of TR1 – at full PSU 30V before this thing kick started at a stable 15.9982MHz.

I removed the top 10nF cap and one 470pF (mine was a different value anyway) from ground., leaving one floating…(aerial!?). So touchy! Just connecting the probe ground can stop it..

17V gives a 1Vpp sine wave – if you don’t move anything!:

3 Transistor Sawtooth Generator / Oscillator

yeah…a really shitty circuit, took fkin ages!! I had to run at 29V and kick start it by pulling and reconnecting a jumper to the emitter of the 2nd pnp tranny. If I dropped voltage below 24V it would stop again…2nd probe would also cut it off on contact. Total pain and batshit noisy. The resistor values aren’t close enough to my transistor 0.7V turn on – got mostly 0.56V at the bases, hence higher voltage req.

LM358 VCO Circuit

This isn’t clear for beginners, but V/2 at pin 5 non-inverting input of amp 2 means you have to add another 2 x say, 10k resistors as a voltage divider to supply the correct voltage at pin 5 – NOT the full PSU voltage (5V) as I did at first – else it won’t work.

The pin 5 100k/51k resistors are the feedback, not the voltage dividers..duh!

With a 47uF cap at pins 1-2 I get the correct outputs:

Kentiger HY-502S Amp

These are good amps for the size, function and cost – if you have a 3-5A, 12V PSU already?!

They can be improved by modding according to:

..agreed, those LEDs are annoying, better if they had been volume levels, not a disco..

Ok, you can buy a classic 90s used amp on Ebay for that £30+ total of PSU also, but if you want small, light (and free electric shocks!), but still good sound, this is worth it for the functions – USB and SD card for MP3; radio, remote control and about a 10W RMS output. Loud enough for most rooms.

I’ll do some tests…

Two Transistor Schmitt Trigger; Converts Analogue Signal to Digital Output

This essential circuit converts an analogue signal to a digital output:

Transistor Schmitt Trigger

This circuit gives a max output of 3.8V digital from a 3.8V sine input;

The Vcc can be no more than 5V else the top threshold of this circuit design is crossed and the output goes to 0V; the input must be no less than 3.7 Vpp AC else the lower threshold won’t be crossed and trigger a change, due to the concept of a Schmitt Trigger:

“It is an active circuit which converts an analogue input signal to a digital output signal. The circuit is named a “trigger” because the output retains its value until the input changes sufficiently to trigger a change. In the non-inverting configuration, when the input is higher than a chosen threshold, the output is high. When the input is below a different (lower) chosen threshold the output is low, and when the input is between the two levels the output retains its value. This dual threshold action is called hysteresis and implies that the Schmitt trigger possesses memory and can act as a bistable multivibrator (latch or flip-flop). There is a close relation between the two kinds of circuits: a Schmitt trigger can be converted into a latch and a latch can be converted into a Schmitt trigger.

Schmitt trigger devices are typically used in signal conditioning applications to remove noise from signals used in digital circuits, particularly mechanical contact bounce in switches.”

I found changing R2 to 30k and increasing Vcc to 5.4V I got a 5V logic level for a 3.6Vpp input:

The closest I got to a 5V, 50% duty cycle square wave was a 3:2 rectangle by changing R1 to 10k and Vcc at 6.8V – an insight to circuit design and limitations like power feed, component stress and stability etc.