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Why sine waves?
If you want the reed relays to turn on and off 120 degrees apart from
each other with insensitivity to the slope of the driving voltage,
ISTM that three 10Hz square waves 120 degrees apart would be much
better.
John Fields has a point. If you are using the signals to drive the reed relays as switches, then putting a sine wave of current through the coils doesn't make much sense.
If you were using the reed relay contacts as - say - three small variable capacitors, a sinsoidal drive would make more sense.
If you actually want sine waves, you might look at one of Analog Devices direct digital synthesis chips. At least one can generate four separate sinusoidal outputs with well-defined phase relationships.
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but it needs 3.3V and 1.8V power rails, and draws 180mA.
You can synchronise single DDS chips to produce separate sine waves with the same frequency in known phase relationships - Winfield Hill had a example on his web-site some years ago - and you might find it better to combine several of the lower-powered Analog Devices DDS chips
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If you don't actually need the sine waves, you could divide down a
32,768Hz watch oscillator in a Xilinx Coolrunner programmable logic device by 546 in the first instance to get yourself an almost 60Hz pulse train, and then decode the outputs of eight-bit counter wired to divide by six to generate three almost 10Hz square waves at 120 degree phase intervals (the first is high for counts 0,1,2 and low for 3,4 and 5, the second high for counts 1,2 and 3 and low for 4,5 and 0).
The first counter needs ten bistables and a decoder, the second three bistables and a decoder, and the three outputs need a decoder each, which sounds like no more than 18 macrocells, so the smallest (64 macrocell) Coolrunner chip could do it. There are probably smaller, cheaper, low power programmable logic parts around, but I've not looked at what's available recently.
You could also use a programmable logic chip to do the digital part of a direct digital synthesis process, and generate three serial bits streams for three serial input DAC's thus duplicating the function of the Analog Devices DDS chips, at the cost of considerably more development effort.
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Driving a relay coil with a sine wave is a bad idea. You cannot be sure at what time in the period the relay will really make or break contact. Especially at this low frequency the relay will have long times to "hesitate" which may detoriate the contacts.
If you do not need the sine, you'd better go for a square wave. If you need the sine you can make squares from it to drive the relay, though you'd better made the squares seperately using the same clock as for the sines.
As for the squares al but the most tiny micros will do. If you need the sines, you'll have to go for a midrange one to make sine waves using a minimum of components.
Power consumption will mainly depend on the on-time of your relays. Three relays will take about 30mA which is high compared to the requirements of a low power micro.
You can of course make it without a micro but you will need much more components for much less accurate results.
Several circuits there including a simple 3-pages oscillator as requested.
You could feed the outputs through LM 339 to drive reed coils.
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On a sunny day (Fri, 5 Nov 2010 04:40:03 -0700 (PDT)) it happened Bill Sloman wrote in :
Makes no sense, program a PIC 12F628 or something like that for 3 x 10 Hz on / off. Software loop. No external parts needed, maybe protection diodes, decoupling caps.
That's fine too, as long as he doesn't need sinewaves. I like the 3- bit shift register. (Don't forget to initialize it--if it comes up with '101', for example...)
Since the OP only asks for 1% frequency stability, and doesn't insist on it, the 7555 is probably good enough.
But - as even James Arthur has had the wit to point out - you haven't made any provision to intialise the state of the shift register, and you've got no idea what bit pattern is circulating through it.
You want a succession of three ones at any one output to be followed by three zeroes, but you've done nothing to make sure that this happens to start with, or keeps on happening thereafter. My counter was at least initialisable, and resets every sixth clock edge.
You could put checking logic onto your shift-register but since you've got to check that 000 or 111 comes up at least once in six clock cycles, you end up adding three-input OR/NOR or AND/NAND gate and a 3- bit counter (or a retriggerable monostable) to do the job, which doubles the component count and looks untidy.
_ Hmmmm/ MY 'HC174 doesn't have any Q outputs :-) ...Jim Thompson
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| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Ding Dong! The Witch is dead. Which old Witch? The Wicked Pelosi!
One pak of 'HC74 plus 1/2 pak of 'HC02 can be made self-correcting. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Ding Dong! The Witch is dead. Which old Witch? The Wicked Pelosi!
Actually only needs ONE gate from the 'HC02 ;-) ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Ding Dong! The Witch is dead. Which old Witch? The Wicked Pelosi!
Where Rt and Ct determine the duration of the Power-On Reset.
(for the mixed startup problem.)
If you want to add a package, you could buffer it with a Schmitt gate, but what happens when the "reset" input oscillates a little? It gets repeatedly reset, until it settles down. ;-)
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