GB2069191A

GB2069191A - Electronic timer apparatus

Info

Publication number: GB2069191A
Application number: GB8002045A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-01-22
Filing date: 1980-01-22
Publication date: 1981-08-19
Also published as: GB2069191B

Abstract

An electronic timer, for example for setting a predetermined interval after the launching of a rocket after which interval a switch is closed on the rocket for firing a flare, comprises a counter (15) Figure 1 arranged to be partly filled from a separate programmer (Figure 3) in a presetting operation. When a switch (21) is closed after the programmer has been disconnected, pulses from a crystal controlled oscillator (14) are used to complete the filling of the counter (15) which then fires a thyristor (25). This causes the charge on a capacitor (26) to operate a fuse or switch (23) for firing the flare. The preset time delay can be set in by switches (45) on the programmer and the switch (21) can either be operated manually when the time delay is to start, or can be arranged to be operated automatically when a rocket starts to spin or to accelerate. The programmer may be coupled inductively to the counter for a presetting operation. <IMAGE>

Description

SPECIFICATION Time delay This invention relates to a variable electronic time delay, and one object is to provide a delay circuit which is repeatably accurate, and yet which need not have a large current consumption, and need not be very bulky or very heavy.

According to the present invention, a variable time delay comprises a counter and a source of clock pulses for the counter, a programmer for presetting the counter in dependence on a desired delay, and a switch arranged to cause clock pulses to be fed to the counter at a selected instant after the counter has been preset.

Thus, if there is a maximum time delay which is the time for the accurate clock pulses to fill the counter from empty, a shorter time delay can be set by partly filling the counter from the programmer and the programmer can include a faster oscillator than the source of clock pulses which of course need not be at an accurate frequency, provided the number of presetting pulses can be accurately counted.

It is preferably possible to disconnect the programmer from the counter, the source of clock pulses and the switch after the counter has been preset, with the counter being arranged to hold its preset count, until it receives a resetting signal; or its count is completed for the clock pulses.

In one convenient form of the invention, there are means responsive to three input signals or input signal levels, two of which enable a trigger for the counter to be toggled on and off, while a second two are used alternately to preset the counter.

The switch could be a manual switch, but in an application where a rocket is to be launched and a secondary function initiated, the preset time delay after launching, there may be a "start" switch responsive to starting of the rocket, for example responsive to its starting to spin, or starting to accelerate with means for holding the switch operated until the time delay has expired. There may be a firing circuit arranged to be closed when the time delay has expired and that conveniently includes capacitance which can be charged when the counter is programmed, and indeed for that purpose it may be possible to use power from the programmer to charge the capacitance.

The invention may be carried into practice in various ways, and one embodiment, together with a modification will now be described by way of example with reference to the accompanying drawings, in which; Figure lisa circuit diagram of a delay circuit, Figure 2 is a diagram showing a programming cycle for the circuit of Figure 1; Figure 3 is a block diagram of a programmer for generating the programme of Figure 2; and Figure 4 is a circuit diagram of a different arrangement for coupling the programmer to the delay circuit.

The delay circuit of Figure 1 includes a Schmitt trigger 11 which is arranged to give "start" signal at 12, when an input signal in excess often volts is received at the input terminal 13 from the programmer of Figure 3. A crystal controlled oscillator 14 is rendered operative when the start signal is received at 12, and that also powers a counter 15 and 16 and resets the counter at 17.Oscillations from the oscillator 14 which constitute clock pulses at a frequency of 32768 Hz are supplied at one input to a NOR gate 17, but cannot be fed to the input 18 of the counter 15, because the other input to the gate 17 carries a 1 signal from the supply at 19 until a "start" switch 21 is switched from its normal position, shown in Figure 1 in which it short circuits a fuse 22 constituting the output, to its operated position in which the second input to the gaite 17 is connected to '0' volts. Before the "start" switch 21 switches over, the inverted output from the NOR gate 17 is a 1, and appears at one input to a NAND gate 22. Thus, inpulses arriving at 13 from the programmer at the other input to the NAND gate 22 are fed to the input 18 of the counter 15.After the "start" switch switches over, provided the input at 13 from the programmer remains at 1, oscillations from the oscillator 14 are passed through the gate 22 to the count terminal 18 of the counter 15.

Thus, after receipt of the "start" signal at 13, the counter 15 can be preset by as many pulses as are supplied by the programmer. Then when the "start" switch 21 is switched over the counter is supplied with pulses from the oscillator 14. They are at a crystal-controlled predetermined rate, and the number necessary to complete the count of the counter 15 will be equal to the complete count, less the number of pulses fed in from the programmer in setting the time delay, and in that way the precise time delay between closing of the "start" switch 21 and energising of the fuse 23 is precisely determined. When the count is complete, the output at 24 changes over and fires a SCR 25 which is connected between a battery of capacitors 26, and one side of the fuse 23.The capacitors 26 are charged from a five volts battery 27 in the delay circuit through a resistor 28 as soon as the setting signal is received at 12 because that biases on a transistor 29. Additional charging current is available from the programmer by way of the input 13, a diode 31, and a resistor 32.

Figure 2 shows the programme for setting the time delay on the timer of Figure 1 which programme is provided by the programmer of Figure 3. The programme of Figure 2 represents the voltage levels between terminals 13 and 33 in Figure 1 as supplied over two lines 34 in Figure 3.

The programmer includes a 500 KHz oscillator 35 which when triggered at 36 from a latch 37 delivers oscillations both brought through a change-over switch 38 to the lines 34 and to a four stage cascade settable counter 39 for counting the number of oscillations delivered to the lines 34. The counter 39 includes a 14 stage binary ripple counter 41 for dividing by 2048, a programmable binary counter 42 operating to base 8 and two programmable decade counters 43 and 44. The counters 42, 43, and 44 can be set by BCD thumb switches 45 to the desired time delay to be measured by the circuit of Figure 1 up to a maximum of 32 seconds in increments of one eighth of a second. The counters 42,43 and 44 feed a decoder 46 which provides an output at 47 to reset the latch 37 and a second latch 48 when the full count of 32 has been achieved.

If the desired time delay in the delay circuit of Figure 1 is to be 10 seconds between closing the "start" switch 21 and firing the fuse head 23, then the number of pulses to be provided over the lines 34 to programme the time delay circuit is 32768 x (32-10) or 720896. The presetting of the counters 42, 43 and 44 in terms of the 10 seconds desired delay means that 720896 pulses are required from the oscillator 35 for the decoder 46 to complete its count and reset the latches 37 and 48. Those pulses can be provided by the oscillator 35 in just over one second.

To programme the delay circuit, a push button 49 is operated on the programmer to switch on the power supply 51, and that has the effect of setting a monostable 52 and the latches 37 and 48 so that a relay 53 is energised and a hold-in contact 54 closes to enable the push button 49 to be released.

Setting of the monostable 52 changes over the bi-pole switch 38 so that the lines 34 connected respectively to the terminals 13 and 33 of the delay circuit are respectively at '0' and 12 volts. That condition is maintained for 100 milliseconds as timed by the monostable 52 and as is apparent from Figure 2, and that has the effect ofturning off the delay circuit of Figure 1 in preparation for being turned on by a pulse which will reset the counter 15.

When the monostable 52 completes its 100 milliseconds, the switch 38 switches back and a monostable 55 is triggered and that provides a 200 milliseconds time delay during which the polarity on the lines 34 is reversed, again as shown in Figure 2. That switches on the delay circuit of Figure 1 and allows time for the circuit to stablise. At the end of the 200 milliseconds delay, the latch 37 is triggered, and that in turn releases the resets on the oscillator 35 and on the various stages of the counter 39. The oscillator 35 now provides its pulses over the lines 34 to preset the counter 15 as described above, until when the desired number has been counted on the decoder 46 and the latches 37 and 48 are reset, the relay 53 releases and the power supply is disconnected.It will be appreciated that the programmer can then be disconnected from the delay circuit, because the count will remain on the counter 15 until the polarity on the terminals 13 and 33 is reversed.

When the "start" switch 21 switches over the preset delay will be timed, and the fuse head 23 will be fired.

In one application, the delay circuit of Figure 1 is mounted in a small rocket, and it is necessary to set a delay time between the moment of launching and the time when a secondary charge is initiated for example, forfiring a flare.

The "start" switch 21 could be on a levered arm micro-switch arranged to be closed by the centrifugal force as the rocket starts to spin on launching which force holds the switch closed. Alternatively, the switch could be an acceleration operated switch arranged to be latched on once closed.

In a modification indicated in Figure 4, instead of having a two line connection between the programmer and the delay circuit, it is possible to provide inductive coupling by means of a transformer 56 receiving the output from the programmer in its primary winding. The output from the programmer will not then be d.c. levels, as with Figure 3, but tones of different frequencies, for example 455 and 470 KHz. The delay circuit then has ceramic filters corresponding to the two frequencies for providing the operating levels to the Schmitt trigger 11, generally as indicated in Figure 4. With such couplings there will not be power available through the filter network to provide the fast charge of the capacitors 26 through the diode 31 and the resistor 32 and the lines containing those components will be removed.

Although the invention has been described as applied to a settable time delay with a certain maximum delay, and with means for reducing that delay in accordance with the desired delay by providing a preliminary count in a programming operation, it is also possible to increase the desired time delay, perhaps up to a week by including additional stages of division between the oscillator and the preset counter.

Claims

1. A variable time delay comprising a counter and a source of clock pulses for the counter, a programmer for presetting the counter in dependence on a desired delay, and a switch arranged to cause clock pulses to be fed to the counter at a selected instant after the counter has been preset.

2. Atime delay as claimed in Claim 1 in which the programmer includes a faster oscillator than the source of clock pulses.

3. Atime delay as claimed in either of the preceding claims in which the programmer can be disconnected from the counter, the source of clock pulses and the switch after the counter has been preset.

4. Atime delay as claimed in Claim 3 in which the programmer is coupled inductively to the counter.

5. A time delay as claimed in any of the preceding claims in which the programmer provides three input signals or input signal levels, two of which enable a trigger for the counter to be toggled on and off while a second two are used alternately to preset the counter.

6. A time delay as claimed in any of the preceding claims in which the switch is a manual switch.

7. Atime delay as claimed in any of Claims 1-5 in which the switch is an automatic switch arranged to be operated in response to movement of a vehicle or body carrying the time delay.

8. A time delay as claimed in any of the preceding claims including a firing circuit arranged to be operated when the time delay has expired.

9. A time delay as claimed in Claim 8 in which the firing circuit includes capacitors arranged to be charged when the counter is programmed.

10. Avariabletime delay arranged substantially as herein specifically described with reference to Figures 1-3 or Figures 1-3 as modified as described with reference to Figure 4, of the accompanying drawings.