I need to generate 3 sinewaves at 10Hz with 120 degree separation. Power is via 4 x "AA" cells.
Each output is to drive two 500R reed relay coils in series. I am hoping for about 40 hours run time.
Stabilty of 0.1Hz is desirable but not necessary.
Can anyone please suggest what is the most straightforward way to achieve this with minimal components?
Mark Weaver
Mark Weaver schrieb:
Hello,
do you really need sinewaves do drive reed relays? What about using 3 squarewaves with 120 degree separation?
Bye
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.
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
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.
-- Bill Sloman, Nijmegen
"Mark Weaver" schreef in bericht news: snipped-for-privacy@news.tpg.com.au...
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.
petrus bitbyter
You could feed the outputs through LM 339 to drive reed coils.
Or he could just use a PIC. That would draw
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.
off.
Even the humble 10F200 would do - with exactly the right number of output pins for the job. The component and pin count is hard to beat.
Regards, Martin Brown
Version 4 SHEET 1 980 680 WIRE 880 -48 0 -48 WIRE 144 80 144 32 WIRE 448 80 448 32 WIRE 752 80 752 32 WIRE 0 128 0 -48 WIRE 64 128 0 128 WIRE 368 128 224 128 WIRE 672 128 528 128 WIRE 0 176 -128 176 WIRE 64 176 0 176 WIRE 272 176 240 176 WIRE 368 176 304 176 WIRE 576 176 544 176 WIRE 672 176 608 176 WIRE 880 176 880 -48 WIRE 880 176 848 176 WIRE -128 208 -128 176 WIRE 144 272 144 224 WIRE 448 272 448 224 WIRE 752 272 752 224 WIRE 0 336 0 176 WIRE 304 336 304 176 WIRE 304 336 0 336 WIRE 608 336 608 176 WIRE 608 336 304 336 WIRE -128 368 -128 288 WIRE -80 368 -128 368 WIRE -128 400 -128 368 WIRE 272 400 272 176 WIRE 576 400 576 176 WIRE 880 400 880 176 FLAG 144 32 0V FLAG 448 32 0V FLAG 752 32 0V FLAG 144 272 0V FLAG 448 272 0V FLAG 752 272 0V FLAG -128 400 0 FLAG -80 368 0V SYMBOL Digital\\dflop 144 80 R0 WINDOW 3 8 168 Invisible 0 SYMATTR InstName A1 SYMATTR Value trise 1e-7 tfall 1e-7 vhigh 6 SYMBOL voltage -128 192 R0 WINDOW 3 24 104 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value PULSE(0 6 0 1E-6 1E-6 .008333 .016666) SYMBOL Digital\\dflop 448 80 R0 WINDOW 3 8 168 Invisible 0 SYMATTR InstName A2 SYMATTR Value trise 1e-7 tfall 1e-7 vhigh 6 SYMBOL Digital\\dflop 752 80 R0 WINDOW 3 8 168 Invisible 0 SYMATTR InstName A3 SYMATTR Value trise 1e-7 tfall 1e-7 vhigh 6 TEXT -8 368 Left 0 !.tran 1 startup uic TEXT 248 424 Left 0 ;OUT1 TEXT 544 424 Left 0 ;OUT2 TEXT 856 424 Left 0 ;OUT3
e:
m .=A0 =A0Vcc
=A0 =A0 =A0 =A0 |
| =A0 =A0 =A0 =A0 =A0| =A0
]--+ =A0 =A0
=A0 =A0 =A0 =A0| =A0
=A0
=A0 | =A0 =A0 =A0 =A0 =A0| =A0
+--[COIL]--+ =A0=A0 =A0 =A0 =A0 =A0 =A0| =A0
IODE>]-+ =A0
=A0 =A0 | =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0
-[COIL]--+
=A0 =A0 =A0 =A0 =A0 =A0
=A0 =A0 =A0 =A0 =A0 =A0 =A0
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...)
-- Cheers, James Arthur
Yikes!
John
e:
m .=A0 =A0Vcc
=A0 =A0 =A0 =A0 |
| =A0 =A0 =A0 =A0 =A0| =A0
]--+ =A0 =A0
=A0 =A0 =A0 =A0| =A0
=A0
=A0 | =A0 =A0 =A0 =A0 =A0| =A0
+--[COIL]--+ =A0=A0 =A0 =A0 =A0 =A0 =A0| =A0
IODE>]-+ =A0
=A0 =A0 | =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0
-[COIL]--+
=A0 =A0 =A0 =A0 =A0 =A0
=A0 =A0 =A0 =A0 =A0 =A0 =A0
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.
-- Bill Sloman, Nijmegen
As shown it isn't too hot for 000 or 111 either. In fact only 3 of the 8 possible initial starting states result in correct behaviour.
D1 = Q1 NOR Q2 would fix it assuming that a couple of illegal states at start up don't cause trouble for whatever is being driven.
I reckon a 6 pin cheap PIC like 10F200 wins this one for ~50c.
Regards, Martin Brown
_ Hmmmm/ MY 'HC174 doesn't have any Q outputs :-) ...Jim Thompson
One pak of 'HC74 plus 1/2 pak of 'HC02 can be made self-correcting. ...Jim Thompson
Actually only needs ONE gate from the 'HC02 ;-) ...Jim Thompson
John Fields wrote: [ASCIImatic] And I modified:
TRIM FOR 60Hz / +-[POT]-[Rt]-+ | | | +-------+ | +--------+ +-|TH OUT|--+--|> 1D|--+ Vcc | |__ | | _| | | +-|TR | | 3Q|O-+--+-[DIODE>]-+ | |_ | | | | | Vcc--|-|R | +--|1Q | +--[COIL]--+ | +-------+ | | _| | | 7555 +--|2D 2Q|-----+-[DIODE>]-+ [Ct] | | | | | +--|2Q | +--[COIL]--+ GND | | _| | +--|3D 1Q|-----+-[DIODE>]-+ | | | | Vcc-+---------------|4D | +--[COIL]--+ | |_ | +----[Rt]----+--|R | | +--------+ [Ct] HC174 | GND
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. ;-)
Cheers! Rich
Have something to add? Share your thoughts — no account required.
Ask the community — no account required