Wednesday, 27 April 2016

LED flasher using relays.

Hey guys.

Just wanna share circuits using relays to flash LED. I researched and found two different designs which both utilises only one relay and some capacitors .

The capacitance of the capacitors is quite big (around 1,000 uF and higher) to yield a low frequency flashing ( if too high then the LED will not appear flashing since it flashes very fast). I did'nt buy the capacitor, instead I salvaged from an old CRT monitor laying around in my room.

Sunday, 17 April 2016

Flip-flop or bistable latching using relays.

Hey guys,

Since I have plenty of relays laying around and dont know what to do with them, I decided to test if using this relays can mimic the flip flop actions of solid state devices such as transistors.

I know that there is already a latching type of relay made into a single package 'latching' relay in the market, but since I have different type of relays which functions as mere simple switching conveyor, I have to use my brain on how to configure these relays into a circuit that can mimic flip flop action.

I came up with two different types of circuitries; design A incorporates two different contacts for SET and RESET actions while design B incorporate only single contact to implement SET and RESET actions.

For readers who don't know what is a flip flop circuit, it is a type of circuit which retains the previous state of its output. For example , say if you have a flip flop circuit operating an LED. The ON and OFF conditions of the LED corresponds to the output state of the flip flop. If we switch ON the circuit, the LED lights up, of course. If we release it back, the LED remains ON. If we apply another press on the switch, the LED goes off. Again if we release the pressing, the LED remains off. This is what flip flop actually does. And due to this ability, it has an ability to store previous input without a need to retain the flow of current, which reduce power consumption and increase operational efficiency. This circuit is used extensively in computer memory and other types of machines that utilizes memory functions.

Here is the circuitry for flip flop using relays;

Update (19th Apr 2016): Unfortunately, Design B proposed above does not work (perhaps it will works at higher input power however higher input power will damage the LED. Updates on 21st Apr 2016: higher power also does not work!). Therefore a revision was made to Design B (see below), but at the expense of power loss since at this new design power is conducted at the triggering flip flop circuitry (Relay 1 and Relay 4) during ON state of the LED. Hopefully this new design will work (update will follow soon...)

Update (21st Apr 2016): Unfortunately, the amended Design B also does not work. I experimented for hours later on and found that the following design for single toggle works, but with oscillating output (LED is blinking). In order to slow down the oscillation, I added up a big capacitance capacitor across Relay 3 coil and the toggling eventually works, The higher the capacitance the slower the oscillation and the easier for you to toggle. Here is the schematic;

Update (22nd Apr 2016): I found a rather simpler circuit for toggling using relays here.
I have made some changes on the proposed circuit such as removing the resistor, introducing LED output and also using two SPDT relays instead of DPDT relays. I have tested and it works excellently, without oscillation. Here is my variant of the circuit.

Thursday, 7 April 2016

Fly swatter stun gun.

Hey guys.

Lately I was obsessed with making a stun gun.

I was particularly interested in fly swatter for the source of high voltage due to being easy to get and very cheap compared to using other high voltage circuitry (like from arc plasma lighter  or plasma globe driver.). It cost me around USD4 for a fly swatter compared to plasma globe (USD8), or arc plasma lighter (USD40) and I also dont have to wait for weeks to get it since its just available at the store in front of my house. (all prices are converted to USD from local currency)

Prior to this I have experimented with salvaged transformers and my self-made cockroft walton multiplier and oscillators (ZVS, 555 timer, joule thief) for making a stun gun but all gave disappointing results such as very thin arc (low current) even though the arc length was quite impressive. This is because for all these designs, I utilized usual 9V batteries which does not give enough current (hence power) to the final output due to its considerably high internal resistance compare to the load circuitry resistance (which subject to its design and chemistry). To add to this, the salvaged transformers were not optimized for the operating point I used.

Based on research I found out that the only optimally designed transformer for stun gun is flyback transformer. Flyback transformer is not only the one you can salvage from old CRT monitor, but the one miniaturised as in plasma globe driver or fly swatter and sometimes appears indistinguishable from common charger transformers (flyback transformer also available in a core-type design instead of the usual shell-type design as in CRT monitor). This type of transformer was designed so its ferrite core will have low coercivity (easily magnetised and de-magnetised to reduce hysterisis loss) and low leakage inductance at high frequency and generally has the ability to step up voltage lower than 10V to several thousands volt.

Fly swatter came to my mind to solve these two problems; getting high current and efficiently transforming voltage lower than 10V to several thousands volt. The reason behind high current from fly swatter is because of the battery it utilizes (which can supply high current at particular voltage) which I reckon is a Lithium polymer rechargeable battery and the specialized step up transformer which intentionally designed for increased efficiency at high voltage and high frequency operation. To my surprise, the voltage supplied by the battery is just 4.25V.

Fly swatter usually output around 1 or 2kV direct current which is sent to the mesh . You may Google and Youtube around to find out how fly swatter looks like. At first glance it seems like a usual tennis racket where the only difference is that the mesh is supplied with high voltage to give a fatal jolt to bugs (which is the primary purpose of its invention, hence the name).

Below is the circuit I adopted (only the high voltage circuitry part) for the fly swatter stun gun;

In the video below, the white stick is the handle of the fly swatter that contains the oscillator (I have removed the wire meshes). Two protruding wires (red and white) are the high voltage direct current output which originally attached to the removed wire meshes. The white plastic former is the spark gap ( I punch a common tape plastic former with two screws which were distanced less than 1mm apart). I found that the smaller the spark gap, the fatter the arc at secondary of high voltage pulse transformer which implies that the transformer can optimally operate at high switching rate (the lesser the spark gap distance, the higher the switching rate). The black taped bulky cylinder is the high voltage pulse transformer, homemade (description in the circuit diagram above).

The length of the arc at the secondary of this transformer is around 1cm (corresponds to voltage around 9kV to 10kV). Enjoy the video!

If you are impatient in waiting the video loading, I attach the final result snapshot below;

(the Powerball (green bulky stuff) and the tape are to fix the high voltage wire terminal in places)

Until next time!

Tuesday, 5 April 2016

Flyback arc driver circuit

Hi everyone.

This post is just a revisit on the Cockroft walton multiplier (CW) discussed before.
I utilised it as an input into the flyback transformer to see how the output looks like.

Some changes were made; I tweaked some component values on the oscillator part so the circuit operates at resonant frequency of the charger transformer (where it rings and produced highest possible output peak voltage as an input into the CW multiplier).

The video below is the outcomes;

The CW is 8 stage with ceramic capacitors (value stated in the circuit diagram below).

The spark produced is around 1.5cm to 2cm in length and is a high voltage direct current.

That's it.