LM 3914 set point controller

cstmwrks · 8th April 2007, 14:17

Well it's Easter Sunday and all it quite around the house. Thanks in part to Dan Fountain I have started looking over my electronics blue book and the 3914 chip that most all my do it yourself electronis for rebreathers has been based on.

Right now I'm looking at my 3914 set point driver with dip switch selectable set point. The driver is used in dot mode with 5 of the outputs going to the dip switch. Turning any one switch on would set the trigger point for the injection timer curcuit.

I built this thing some 6 years ago and it still sets out in the shop waiting for feild testing. The lm358 op amp has been suspect in getting proper signal output to the driver. Having read the latest posts on better op amps I'm going to have to upgrade and continue with more testing. Also the interval timer gave out after some 24 hours of running. The timer curcuit was tested as a stand alone module and then plugged into the dip switch that triggers the timer. As I recall it was a soft fail. It did not just up and stop working but would be erratic untill it stopped all together.

Not to be discouraged I have noted from looking over a Velman interval timer kit that there circuit contained a few more diodes than my timer set up had. My hope is the timer died from a built in flaw and the folks over at Velman know just a tad bit more on building a robust and stable analog circuit than I do.

Voting logic. This was the next step with the 3914 based controller. I have not made it past the " thinking about it stage" but it would use three sensors and all the selected dot segments would turn on an optically coupled MOSFET switch that would supply a power signal of say 1.2 volts to a summing amp. The sum of any two drivers would be the voltage used to trigger the interval timer. At this point the voltage switch design has not got much thought and I'm not real fond of the 741 style window comparator. If I had more knowledge of basic IC chips there may very well be a simple chip out there that can do this, or it has to be designed.

**wedivebc** · 8th April 2007, 15:09

Quote: (Originally Posted by cstmwrks)

Well it's Easter Sunday and all it quite around the house. Thanks in part to Dan Fountain I have started looking over my electronics blue book and the 3914 chip that most all my do it yourself electronis for rebreathers has been based on.

Right now I'm looking at my 3914 set point driver with dip switch selectable set point. The driver is used in dot mode with 5 of the outputs going to the dip switch. Turning any one switch on would set the trigger point for the injection timer curcuit.

I built this thing some 6 years ago and it still sets out in the shop waiting for feild testing. The lm358 op amp has been suspect in getting proper signal output to the driver. Having read the latest posts on better op amps I'm going to have to upgrade and continue with more testing. Also the interval timer gave out after some 24 hours of running. The timer curcuit was tested as a stand alone module and then plugged into the dip switch that triggers the timer. As I recall it was a soft fail. It did not just up and stop working but would be erratic untill it stopped all together.

Not to be discouraged I have noted from looking over a Velman interval timer kit that there curcuit contained a few more diodes than my timer set up had. My hope is the timer died from a built in flaw and the folks over at Velman know just a tad bit more on building a robust and stable analog curcuit than I do.

Voting logic. This was the next step with the 3914 based controller. I have not made it past the " thinking about it stage" but it would use three sensors and all the selected dot segments would turn on an optically coupled MOSFET switch that would supply a power signal of say 1.2 volts to a summing amp. The sum of any two drivers would be the voltage used to trigger the interval timer. At this point the voltage switch design has not got much thought and I'm not real fond of the 741 style window comparator. If I had more knowledge of basic IC chips there may very well be a simple chip out there that can do this, or it has to be designed.

What is the advantage of using analog circuits for set point control over using a digital programable unit such as a pic?

cstmwrks · 8th April 2007, 16:12

Quote: (Originally Posted by wedivebc)

What is the advantage of using analog circuits for set point control over using a digital programable unit such as a pic?

At no point did I ever say there is any advantage. There are some out there who happen to like the "old" way of doing things. The old MK 16 was a class design in analog electronics. Modern minds far more brilliant than mine had paid hi respect to the designers that made the horseshoe board decades ago.

Not to say that what ever I come up with will ever get paid any respect at all, let alone hi respect. Its just interesting. From my point of veiw it seams everyone is on the digital bandwagon. Nothing wrong with it at all... its the way things are done these days. Still I tend not to follow with the crowds and I can not recall anyone having come up with a simple analog voting controller.

Again, not saying that I have come up with a grand idea by any means. But it is some thing that I intend on tweeking untill it either works to my expectations or I trash the project. And I've often found that if I talk about some thing in the open I tend to get little bits of insight and input from other people with there own knowledge and experiance.

Tom Rose · 8th April 2007, 17:53

Quote: (Originally Posted by wedivebc)

What is the advantage of using analog circuits for set point control over using a digital programable unit such as a pic?

Until recently, the advantage was ease of use and price of getting into digital systems.

Cost and learning curve....especially the "fear factor" of having to program. I have seen it stop even engineers cold while a 14 year old just goes forward. And then there was the startup costs of digital programing. Compilers, special boards etc. A bit confusing for those without the right background.

For a while now there has been a system...(I was unaware of) called the picaxe. Now you can easily and cheaply go digital or even more cheaply and accurately go a combination of digital and analog. If you already own a computer with a serial port you can get in for less than 20 bucks.

The other day I started designing the circuits and writing psudo code (while my order for a couple dozen Picaxes came in Half of them 18 x and half of the them 8 M.

I have already designed Printed Circuit Board for a 8 m system with a dual op amp that should have a final cost of less than 10 bucks including the picaxe, the op amp, the resistors, and the red/green led. Due to time constraints, I will not be testing for two weeks. The PCB is just over 1 inch square right now. Battery supply is three aaa cells. Yes I am going for compact. If I like the design, I will go to surface mount to make it smaller.

And yes, I will publish the board pattern and code. And No, I will not build them for sale....

Tom

cstmwrks · 8th April 2007, 21:23

Quote: (Originally Posted by Tom Rose)

Cost and learning curve....especially the "fear factor" of having to program.

Tom

This would be one point in my own avoiding of digital, first you have to design the electronics AND you have to write code as well. I understand that they are not very complex systems, but still when troubles arive will it be from the hardware or the software?... or both...

Now Tom has went an thrown a real wrench into my thinking.. Thanks Tom, I hope your happy with yourself!! I just looked at the picaxe info on the web.... wow.. digital for the price of a happy meal.

Tom Rose · 9th April 2007, 04:35

Quote: (Originally Posted by cstmwrks)

This would be one point in my own avoiding of digital, first you have to design the electronics AND you have to write code as well. I understand that they are not very complex systems, but still when troubles arive will it be from the hardware or the software?... or both...

Now Tom has went an thrown a real wrench into my thinking.. Thanks Tom, I hope your happy with yourself!! I just looked at the picaxe info on the web.... wow.. digital for the price of a happy meal.

Yes digital for the cost of a happy meal...well put....aint life grand....so much to explore...

Tom

Duncan Price · 9th April 2007, 08:29

I had a similar idea after working on my bar graph HUD (still not working). Tom kindly corresponded with me on this and recommended that I go digital. As a better programmer than electronics guru he may have a point...

PS. I using instrumentation amps rather than single op amps. More stable.

cstmwrks · 9th April 2007, 14:24

Quote: (Originally Posted by Duncan Price)

I had a similar idea after working on my bar graph HUD (still not working). Tom kindly corresponded with me on this and recommended that I go digital. As a better programmer than electronics guru he may have a point...

PS. I using instrumentation amps rather than single op amps. More stable.

Aha!.. so our kind and mild mannered Tom Rose is beating the drum of the digital DEVIL! And to think I almost fell for it.
What op amps did you use? As I recall, digital or analog there was still an amp involved before the signal was sent to an AD.

8th April 2007, 14:17	#1 (permalink)
cstmwrks The old ways still work. Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Sep 2006 Location: Boise Idaho Posts: 238	LM 3914 set point controller Well it's Easter Sunday and all it quite around the house. Thanks in part to Dan Fountain I have started looking over my electronics blue book and the 3914 chip that most all my do it yourself electronis for rebreathers has been based on. Right now I'm looking at my 3914 set point driver with dip switch selectable set point. The driver is used in dot mode with 5 of the outputs going to the dip switch. Turning any one switch on would set the trigger point for the injection timer curcuit. I built this thing some 6 years ago and it still sets out in the shop waiting for feild testing. The lm358 op amp has been suspect in getting proper signal output to the driver. Having read the latest posts on better op amps I'm going to have to upgrade and continue with more testing. Also the interval timer gave out after some 24 hours of running. The timer curcuit was tested as a stand alone module and then plugged into the dip switch that triggers the timer. As I recall it was a soft fail. It did not just up and stop working but would be erratic untill it stopped all together. Not to be discouraged I have noted from looking over a Velman interval timer kit that there circuit contained a few more diodes than my timer set up had. My hope is the timer died from a built in flaw and the folks over at Velman know just a tad bit more on building a robust and stable analog circuit than I do. Voting logic. This was the next step with the 3914 based controller. I have not made it past the " thinking about it stage" but it would use three sensors and all the selected dot segments would turn on an optically coupled MOSFET switch that would supply a power signal of say 1.2 volts to a summing amp. The sum of any two drivers would be the voltage used to trigger the interval timer. At this point the voltage switch design has not got much thought and I'm not real fond of the 741 style window comparator. If I had more knowledge of basic IC chips there may very well be a simple chip out there that can do this, or it has to be designed. __________________ Why you ask... well it's not like I have anything better to do. Last edited by cstmwrks : 8th April 2007 at 16:43. Reason: after thoughts
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8th April 2007, 15:09	#2 (permalink)
wedivebc Dave Tomblin Current Rebreather/s: Megalodon Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Other CCR Join Date: Feb 2005 Location: Vancouver Island BC Canada Posts: 1,508	Re: LM 3914 set point controller Quote: (Originally Posted by cstmwrks) Well it's Easter Sunday and all it quite around the house. Thanks in part to Dan Fountain I have started looking over my electronics blue book and the 3914 chip that most all my do it yourself electronis for rebreathers has been based on. Right now I'm looking at my 3914 set point driver with dip switch selectable set point. The driver is used in dot mode with 5 of the outputs going to the dip switch. Turning any one switch on would set the trigger point for the injection timer curcuit. I built this thing some 6 years ago and it still sets out in the shop waiting for feild testing. The lm358 op amp has been suspect in getting proper signal output to the driver. Having read the latest posts on better op amps I'm going to have to upgrade and continue with more testing. Also the interval timer gave out after some 24 hours of running. The timer curcuit was tested as a stand alone module and then plugged into the dip switch that triggers the timer. As I recall it was a soft fail. It did not just up and stop working but would be erratic untill it stopped all together. Not to be discouraged I have noted from looking over a Velman interval timer kit that there curcuit contained a few more diodes than my timer set up had. My hope is the timer died from a built in flaw and the folks over at Velman know just a tad bit more on building a robust and stable analog curcuit than I do. Voting logic. This was the next step with the 3914 based controller. I have not made it past the " thinking about it stage" but it would use three sensors and all the selected dot segments would turn on an optically coupled MOSFET switch that would supply a power signal of say 1.2 volts to a summing amp. The sum of any two drivers would be the voltage used to trigger the interval timer. At this point the voltage switch design has not got much thought and I'm not real fond of the 741 style window comparator. If I had more knowledge of basic IC chips there may very well be a simple chip out there that can do this, or it has to be designed. What is the advantage of using analog circuits for set point control over using a digital programable unit such as a pic? __________________ Cheers, Dave.... Man is the only animal burdened with the knowledge he will eventually die
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8th April 2007, 16:12	#3 (permalink)
cstmwrks The old ways still work. Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Sep 2006 Location: Boise Idaho Posts: 238	Re: LM 3914 set point controller Quote: (Originally Posted by wedivebc) What is the advantage of using analog circuits for set point control over using a digital programable unit such as a pic? At no point did I ever say there is any advantage. There are some out there who happen to like the "old" way of doing things. The old MK 16 was a class design in analog electronics. Modern minds far more brilliant than mine had paid hi respect to the designers that made the horseshoe board decades ago. Not to say that what ever I come up with will ever get paid any respect at all, let alone hi respect. Its just interesting. From my point of veiw it seams everyone is on the digital bandwagon. Nothing wrong with it at all... its the way things are done these days. Still I tend not to follow with the crowds and I can not recall anyone having come up with a simple analog voting controller. Again, not saying that I have come up with a grand idea by any means. But it is some thing that I intend on tweeking untill it either works to my expectations or I trash the project. And I've often found that if I talk about some thing in the open I tend to get little bits of insight and input from other people with there own knowledge and experiance. __________________ Why you ask... well it's not like I have anything better to do. Last edited by cstmwrks : 8th April 2007 at 16:40.
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8th April 2007, 17:53	#4 (permalink)
Tom Rose Still Learning Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Prism Topaz Other CCR Home Build Join Date: Oct 2005 Location: USA,North Carolina Posts: 331	Re: LM 3914 set point controller Quote: (Originally Posted by wedivebc) What is the advantage of using analog circuits for set point control over using a digital programable unit such as a pic? Until recently, the advantage was ease of use and price of getting into digital systems. Cost and learning curve....especially the "fear factor" of having to program. I have seen it stop even engineers cold while a 14 year old just goes forward. And then there was the startup costs of digital programing. Compilers, special boards etc. A bit confusing for those without the right background. For a while now there has been a system...(I was unaware of) called the picaxe. Now you can easily and cheaply go digital or even more cheaply and accurately go a combination of digital and analog. If you already own a computer with a serial port you can get in for less than 20 bucks. The other day I started designing the circuits and writing psudo code (while my order for a couple dozen Picaxes came in Half of them 18 x and half of the them 8 M. I have already designed Printed Circuit Board for a 8 m system with a dual op amp that should have a final cost of less than 10 bucks including the picaxe, the op amp, the resistors, and the red/green led. Due to time constraints, I will not be testing for two weeks. The PCB is just over 1 inch square right now. Battery supply is three aaa cells. Yes I am going for compact. If I like the design, I will go to surface mount to make it smaller. And yes, I will publish the board pattern and code. And No, I will not build them for sale.... Tom __________________ The 50-50-90 rule: Anytime I have a 50-50 chance of getting something right, there's a 90% probability I'll get it wrong the first time. www.atlimp.com
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8th April 2007, 21:23	#5 (permalink)
cstmwrks The old ways still work. Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Sep 2006 Location: Boise Idaho Posts: 238	Re: LM 3914 set point controller Quote: (Originally Posted by Tom Rose) Cost and learning curve....especially the "fear factor" of having to program. Tom This would be one point in my own avoiding of digital, first you have to design the electronics AND you have to write code as well. I understand that they are not very complex systems, but still when troubles arive will it be from the hardware or the software?... or both... Now Tom has went an thrown a real wrench into my thinking.. Thanks Tom, I hope your happy with yourself!! I just looked at the picaxe info on the web.... wow.. digital for the price of a happy meal. __________________ Why you ask... well it's not like I have anything better to do. Last edited by cstmwrks : 8th April 2007 at 21:34.
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9th April 2007, 04:35	#6 (permalink)
Tom Rose Still Learning Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Prism Topaz Other CCR Home Build Join Date: Oct 2005 Location: USA,North Carolina Posts: 331	Re: LM 3914 set point controller Quote: (Originally Posted by cstmwrks) This would be one point in my own avoiding of digital, first you have to design the electronics AND you have to write code as well. I understand that they are not very complex systems, but still when troubles arive will it be from the hardware or the software?... or both... Now Tom has went an thrown a real wrench into my thinking.. Thanks Tom, I hope your happy with yourself!! I just looked at the picaxe info on the web.... wow.. digital for the price of a happy meal. Yes digital for the cost of a happy meal...well put....aint life grand....so much to explore... Tom __________________ The 50-50-90 rule: Anytime I have a 50-50 chance of getting something right, there's a 90% probability I'll get it wrong the first time. www.atlimp.com
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9th April 2007, 08:29	#7 (permalink)
Duncan Price Sump Monster Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Feb 2005 Location: Wells, Somerset, UK Posts: 335	Re: LM 3914 set point controller I had a similar idea after working on my bar graph HUD (still not working). Tom kindly corresponded with me on this and recommended that I go digital. As a better programmer than electronics guru he may have a point... PS. I using instrumentation amps rather than single op amps. More stable.
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9th April 2007, 14:24	#8 (permalink)
cstmwrks The old ways still work. Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Sep 2006 Location: Boise Idaho Posts: 238	Re: LM 3914 set point controller Quote: (Originally Posted by Duncan Price) I had a similar idea after working on my bar graph HUD (still not working). Tom kindly corresponded with me on this and recommended that I go digital. As a better programmer than electronics guru he may have a point... PS. I using instrumentation amps rather than single op amps. More stable. Aha!.. so our kind and mild mannered Tom Rose is beating the drum of the digital DEVIL! And to think I almost fell for it. What op amps did you use? As I recall, digital or analog there was still an amp involved before the signal was sent to an AD. __________________ Why you ask... well it's not like I have anything better to do.
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