Remote radio telescope to 27MHz

I therefore propose plans for your information ... or your inspiration ...

On each of the following frameworks include graphics and diagrams necessary to complete a circuit board. By clicking through, you will enter into detailed drawing of the PCB corresponding with which you can set the mask.

Principle of this remote 27MHz:

The control box has four buttons that correspond to the four possible directions for editing and a switch to indicate the speed of movement. The RF signal transmitted is frequency modulated by a four frequency BF whose presence or absence code the direction and speed of editing.
The receiver decodes the signal with a system of filters and detectors that checks frequency BF. The command is identified and transmitted to the drive motor in question (right ascension and declination). Two speeds are possible correction. The slow speed corresponds to a movement of the object in the telescope field with the speed of the diurnal motion. Fast speed is 10 times the speed of daily movement.

Warning! The radio remote control system I describe below emits radio signals to a frequency band of 27MHz. In France, the use of this frequency range is reserved for the CB and remote controls. The remote control system the following is not registered but I consider that the power level is negligible because it emits very low. However, I did not measure and I can not guarantee that it is acceptable to the regulations in force in France. Therefore, before using this device, you should check its legality.

The radio transmitter 27MHz:

Information is transmitted by an audio signal that is modulated by an oscillator frequency 455kHz differential formed by T1, T2 and the IF filter 4101A.

This signal is then mixed with that of a 27MHz crystal oscillator circuit by the S042P. In fact, the quartz must have a resonant frequency lower than 455kHz we want to make some suppliers qualify for receipt of quartz. In this remote control system, the quartz transmitter and receiver have the same resonance frequency.

At the exit of SO42P, the filter formed by C5 and Tr2 to select the signal whose frequency is the sum of the 455kHz signal and the oscillation frequency of the quartz. It is then amplified by T3 and applied in an oscillating circuit including the coil is printed on the circuit.

The radiation is provided by a small piece of copper wire serving as an antenna and the natural radiation of the coil printed.

Note the presence of a strap is a simple piece of wire.

I make the setting of this transmitter by capturing its influence with a coil that I first connected to the input of an oscilloscope. Then I act on the capacitor Cv to maximize the signal amplitude displayed then I do the same with the transformer Tr2.

For these settings, it is essential to use an insulated screwdriver because the approach of a classic metal screwdriver influence the oscillating circuit and make it impossible to fine tune. I made my screwdriver with an insulated strip epoxy printed circuit board that I got rid of the copper layer and which I sharpened the end with a wheel.

Then I connect the coil to a frequency exactly and I adjust the frequency to the desired value by acting on the transformer

The multivibrator transmitter 27MHz

The order to be transmitted is encoded as 4-BF frequencies. By their presence or their absence, they comprise a 4 bit word. So if we transmit only the frequency 1 the compound word is 1000.
In fact, I decided to issue a frequency for each order. Its presence therefore shows that an order is transmitted. To do this, do not forget to solder the jumper shown in the diagram below. It is the combination of the three other frequencies, chosen by the control circuit of the transmitter, which means the order concerned. The system can identify eight different orders (1000-1111).
Here are the values ​​that I use for these frequencies:
F1 = 660 Hz
F2 = 760 Hz
F3 = 870 Hz
F4 = 1000 Hz
The generation frequency is provided by four astable multivibrators designed with circuits ICM75555. The frequency of each can be adjusted through the potentiometer associated with it.
IMPORTANT: For components IC1 to IC4, it is important not to use the CMOS version (ie ICM7555) because the principle of this device is incompatible with this technology. I lost a lot of time and energy before you learn.
The first circuit I built to this plan worked very well with NE555 but I wanted to try the ICM7555 to a new realization. Then I found a malfunction unpleasant and incomprehensible. The multivibrators could start instantly (that's what I wanted) or take several seconds to run, and this time was different every time!
The explanation of this problem lies in the rapid establishment of the supply voltage. In the absence of control, this circuit is not powered. Pressing a button causes a sudden power circuits of the issuer that is incompatible with CMOS circuits. Such a case of fast power may cause malfunction of CMOS logic circuits that can take states "logical" inconsistent with their normal functions.

 

The control circuit of the transmitter 27MHz

 

Wiring the Transmitter 27MHz

 

Receivers 27MHz

This device comprises two receivers. There's a motor that controls the right ascension, it is placed on the base of the telescope. The second controls the motor declination, it is installed on the tube of the instrument.
Three circuits are the same on both devices, it's food, receiver and filter circuit and detection.
The power of the receiver 27MHz
This power supply includes a limiter battery discharge similar to that which is present on receiver power 300MHz.
This tour also includes the decoder (IC1) which controls the four LED indicator of management controls.
The illumination of the LED D8 shows the state of battery charge. She died when the load is insufficient. Therefore, the discharge limiter will not be long to interrupt power to the receiver.

The receiver 27MHz

This module must be mounted on a printed circuit on both sides. Both sides are connected by three straps on both sides. Each consists of a copper wire soldered on both faces. They are located under the integrated circuits IC1 and IC2 IC3.
To be functional, the receiver must be connected to an antenna summary. A piece of wire of about fifty centimeters pinned on the telescope (wooden) may well do the trick.
After mounting the circuit, it should be given to the frequency of the transmitter. This is done by measuring the voltage of the intermediate frequency (455 kHz) between points P1 and P2 with an oscilloscope. It then connects to an antenna (a piece of thread) and the supply voltage is switched on and adjusted the transmitter successively transformers Tr1, Tr2 and Tr3 insulation with a screwdriver in order to increase maximum tension displayed by the oscilloscope.
To adjust the receiver, the oscilloscope is connected to the wire of the resistor R5 which is connected to capacitor C5. It activates the transmitter and then we look to get the maximum signal by acting on the transformer Tr4.
For the final adjustment, connect the input of the oscilloscope to the output signal BF. It activates the transmitter by pressing the button B4 in "Fast Forward". By acting on the variable resistor Rv, you set the level of the audio signal so that it is no maximum saturation (in fact, a slight saturation can be beneficial to the sensitivity).

Filters and detection receiver 27MHz

This device isolates an AF frequency filter with a state variable and detects a diode rectifier. On output, it provides the signal that Fx is the low state when the corresponding frequency is detected. This circuit includes two sets of filtering and detection. Thus it takes two of these circuits by the receiver to interpret the four frequencies that encode the BF command.
On the PCB, the two modules are separated by independent power IC2.Celle it provides a fictitious mass to operational amplifiers. These work well as if they were connected to a power symmetric.
The filter must first be tuned to the desired frequency by acting on Rv.
Sometimes we use our telescopes at temperatures as low as -20 ° C. For this circuit work properly in these conditions we learned that we must choose ceramic package tours to IC1 and IC1 '.
Please do not forget the strap.

 

Decoding receiver 27MHz RA

This circuit interprets the detected signals to control the drive motor. In addition, it has an audible alarm to indicate that the smooth area will soon arrive at the end of the race.
Again, the operational amplifiers IC1 and IC2 should be chosen with a ceramic package.

Motor control of right ascension

The potentiometer P (model 10 laps) allows fine tuning of the engine speed and adjustable resistance Aj is used to adjust the maximum engine speed at quick fixes.

 

Wiring the Receiver 27MHz right ascension

This pattern does not show the 1 Amp fuse must be placed between the power supply and battery.
The direction of rotation we get for the motor is suitable for our horses. To run the engine in reverse, just swap the son of gray and black.

 

Decoding Receiver 27MHz declination

In addition to the function module similar to the RA found on this circuit the generator of the frequency drift by which the user can cause a drift of the instrument allows for variation to follow a wandering star (eg a comet) .
I recommend choosing to IC1 and IC2 circuits with ceramic packages.

 

Declination motor control

The rotary switch selects between the absence of drift motion in declination and three speed ranges for this movement. The fine adjustment being provided by the potentiometer 10 laps earlier.

 

Wiring the Receiver 27MHz declination

This pattern does not show the 1 Amp fuse must be placed between the power supply and battery.

By Serge Bertorello