Yes, I've understood this point since you first mentioned it.huttojb said:The reason for not using the PIC for the timing is I'm running out of inturrupts at the moment, as you aware there is a limited amount of interupts you can use so I need these for other task.
Yes, I've understood this point also since you first mentioned it.huttojb said:I understand what your saying with having one timer per PIC but I don't think this would work for multiply switching.
i.e. Just say it is 1 second (I think it's lower then this but for a figure) I switch one on then start the timer, 900mS later I switch another one on, the timer runs out and then switches both off, therefore the 1st one was on for the required 1s, the 2nd for only 100mS????
Would servicing the interrupts take this long?huttojb said:Also as I've got High Level inturutps I may go away and do something else and not poll the timer for another second. So therefore the switch has been on for over 2 seconds??
I suggest that you use 10M for the long time so the capacitor will be in the order of 150 nF.huttojb said:The timer you gave me is the one I need and will cost penies, I don't have to worry about any timing issues because of the hardware, the only issue I have with the timer is; with the two 100k resistors the input pulse needs to be hi for approx 400mS. I need the input pulse to be approx 10mS, this is the reason I changed the 100k after the diode to 470 Ohms. Can you advise the correct way of acheving this??
Jason
The 74HC14 is very fast and much faster than you need. I would use either the 4584 or the 40106 Schmitt Triggers.huttojb said:Would the Hex invertor,74HC14N DIP14 2-6V be able to do the schmitt trigger and the invertor for me?
Jason
Yes, the MC14584 is the one I suggested (ie. the 4584) Motorola add a 1 in front. You could use the MC14584 ICs as inverters, but, in Australia, the 4069 is cheaper than the 4584. That's why I suggest you use 9 4584's and 8 4069's.huttojb said:Thank you, the only one I can find in UK RS Components is Hex schmitt trigger,MC14584BCP, will this one acheive what I want.
As I said yesterday, the 74HC series is faster than you need.huttojb said:Also I can't find the 4069 Hex inverter in RS so would Hex invertor,74HC14N DIP14 2-6V work.
I said you need 150 nF. You used 50 nF.huttojb said:I placed your values in Multisim and don't come out with the results you expected.
I suggest you measure it as you will save money if all you need is a pair of timers rather than 50 delay units.huttojb said:Sorry I forgot to answer the pull in time for the MPS, yeah I agree it is probably much less then 1second but that was the greatest time I would drive the MSP. I agree is maybe as little as 100mS - 300mS but this is something I haven't monitored.
You don't need a power transistor. I would use an N channel MOSFET such as the 2N7000.huttojb said:Can you confirm I have done this correctly (see attachment)
This cct will be switching TIPL770 Power transistor, would this be able to drive the Base of this transistor????
Yes you will need a series resistor. I'll draw a circuit once you resolve the MPS operate time issue.huttojb said:Will I need to put any resistors in series??? A cct diagram would be nice!
You're welcome.huttojb said:Thanks again Len for all your help.
I'm confused. You said in an earlier post that the MPS operates from 12 Volt and has a coil resistance of 120huttojb said:The N channel MOSFET such as the 2N7000 is 0.2A, when I operate the MPS it pulls up to 2A, thats the reason I said I'll use the TIPL770 Power transistor (this is rated at 2.5A), please advise?
There must be something wrong with your simulation., The circuit will work with any capacitor value.huttojb said:When I used your 150 nF C value it didn't work so I changed it to the 50 nF
Good.huttojb said:I agree I have to monitor the timing of the MPS and operate this at this timing + a Bounce time.
ljcox said:There must be something wrong with your simulation., The circuit will work with any capacitor value.
QUOTE]
It works but the timeing is all wrong (well on the simulation) I will probably for the first module have to put the Capacitor on flyleads so I can change it to get the right time base.
Jason
Thanks again for all your time and response.
No. If you look at the data sheet it has a maximum Vce sat of 2.5V at Ic = 2.5 A with a base current of 0.5A.huttojb said:Honestly I don't know where I got 120 Ohms from. I've just measured the coil again and it measures at 5 Ohms. So Like I worked out before 12/5 = 2.4A. (must of been thinking about something else)
When I monitor it on the power supply and put a current limit to 2A, it seems to give constant voltage supply and doesn't trip the power supply out.
So if I use a power transistor would the TIPL770 Power transistor work?
Did you see the attachment to my last post?huttojb said:It works but the timeing is all wrong (well on the simulation) I will probably for the first module have to put the Capacitor on flyleads so I can change it to get the right time base.ljcox said:There must be something wrong with your simulation., The circuit will work with any capacitor value.
Yes, I thought the size and cost of the relays might be an issue, but I like to give people options so they can weigh them up and choose.huttojb said:Len
Good design and I can sort of follow what you mean, I think the cost of the relay may make this as a dis-advantage. The first design you come up with works and the cost isn't that bad.
I did not bother, the STB100NFO4-1 should be adequate, particularily if they are free.huttojb said:Just a couple of questions, can you look at http://rswww.com and see if you can find me a transistor or MOSFET I can use?? I'm struggerling trying to find them
Use 220 nF and a 6M8 resistor. These give about the same time constant.huttojb said:Also I can't find a 150nF Capacitor on the RS website?
You are confusing the max gate voltage with the gate voltage necessary to turn the FET on. If you study the data sheet, you will see a graph showing that for a Vgs of 2.5 Volt, the Id is about 40 Amp (from memory).huttojb said:And a question about using MOSFET's, I've got 1000's of STB100NF04L-1(035Y)N-CHANNEL 40V - 0.0036 W - 100A I2PAK
STripFET™ II POWER MOSFET, Obviously these will be rated very high for this application, but they free??? Doesn't there have to be biased at around 17V or something like that????
See comment above.huttojb said:If I can use these FET's how would I bias them??
Are you still intending to measure the operate times of a few MPSs?
Use 220 nF and a 6M8 resistor. These give about the same time constant.
Besides, if you look at the calculations I posted, you will see that the Schmitt Trigger ICs have a wide spread of threshold voltage so you will have to choose R and/or C in order to set the delay at about 1.5s. If you don't understand this point, let me know and I'll explain in more detail. It is a statistical issue.
You are confusing the max gate voltage with the gate voltage necessary to turn the FET on. If you study the data sheet, you will see a graph showing that for a Vgs of 2.5 Volt, the Id is about 40 Amp (from memory).
So if you drive the gate from the output of the inverter, (ie. 5 Volt) it will be more than adequate for your application.
Yes, but don't neglect putting a diode across the MPS coil to protect the MOSFET.huttojb said:So If I put the Source to ground, the drain to the low side of the MPS and then drive the gate directly from the invertor, this should work????? I've attempted this before and got into all sorts trouble. I'll Try again.
Jason
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