This a counter-based solution mentioned before, based on something for another thread. The CD4060 is an CMOS oscillator and 14-stage divider. This means that the square wave at Q14 is 16,384 times slower than the oscillator frequency. This means that the for a time delay equivalent to the other circuits, the timing components can be 8192 times smaller. The 4060 is one of the greatest CMOS parts ever. However, it is standard CMOS so its output stage is good for only 1-2 mA and it cannot drive the SSR directly.

When the Q14 output is low, transistor Q1 is on and the SSR is on. I added an LED so you can see that the part is in the timing phase.

A closed switch holds the device in reset, so all outputs are low, the SSR is on, and the LED is off. When all switches are open, the oscillator starts and the LED starts blinking at about 1 Hz. After 8192 oscillator cycles, Q14 goes high. This turns off Q1 and the SSR, and freezes the oscillator through D1 (the 4060 does not have an enable/disable pin). When any switch closes it resets the counter, turning on the SSR.

C2 and R3 form a power-on-reset. When the circuit is powered on it runs through a 5 minute fan cycle even if all switches are open.

ak
View attachment 146929

I'm not real sure what makes this one work. Pin 11 is supposed to be oscillator input, and 9 and 10 oscillator outputs... is this the feedback that was described in some places? Does R1/C1 determine the frequency of the oscillator? And what is the theoretical frequency? I'm not sure what order the stages go in, but I'm assuming the 1 Hz of the LED is because it's slowed down so many steps from the oscillator.

If I wanted to omit the power on cycle, would I just leave out C2 and R3?

 

Most of your questions are answered by the datasheet.

If I wanted to omit the power on cycle, would I just leave out C2 and R3?

Unfortunately, no. A common "feature" of using this part in this way is that the reset state (a 0 at all outputs) is part of the timing mode and the ON state for the output device.

ak

 

Most of your questions are answered by the datasheet.

Unfortunately, no. A common "feature" of using this part in this way is that the reset state (a 0 at all outputs) is part of the timing mode and the ON state for the output device.

ak

Well, lots of good ideas to play with on the bench first. Many ways to skin the cat. Looks like I need to put together an order with Mouser or someone for parts. From an individual point of view, it's cool that there are ICs out there that have so many possibilities, but are so cheap to buy!

I asked in a woodworking group about delaying the dust collector shutdown, and the general opinion seemed to be that it's not really needed for the motor. One guy was advised by the company he bought the DC from that the start capacitor would last longer if he used a delay to prevent it from starting as much. But I think whoever gave that advice overestimated how many times it would be shut down and restarted.

There may be more value in a short delay just to make sure the ducts get cleared of all the chips and dust before it shuts down.

Anyway, thanks again for all your help!
Keith

 

Startup capacitor life is a real thing. Over the years, I've put two startup capacitors in my air conditioning compressor. A shorter time extension, like 30 seconds or 1 minute, makes any of the non-counter methods much more viable. Please keep me posted.

ak

 

Last one until the next one. I think you get the idea by now.

ak
View attachment 146910

Hello... finally got a chance to breadboard a couple of these circuits. On this one with the Schmitt trigger inverters, I was wondering why you show 5 inverters in series. Logically you would need two, right? When a switch is closed, input 1 goes high, output 2 low which is input to the 2nd stage, causing output to go high and trigger the SSR.

I got the SSR from Amazon, and couldn't find a datasheet there, but a similar one from Mouser shows 7.5 mA trigger current on the input. At 9V that's about 68 mW. The CD4060 datasheet shows "Device Dissipation per Output Transistor" of 100 mW. Is that the right spec to compare? Sounds like that would be per inverter.

Anyway, is that the reason for using multiple inverters on the 2nd stage? Better ability to drive the SSR input? Come to think of it, I don't have the actual datasheet for the SSR, and for a China-made SSR, it could possibly draw more current than expected, so it might be good to be on the safe side.

 

Fer cripes sake... just noticed I was looking at the wrong datasheet. Had the hex schmitt trigger inverter one up and also the one for the counter/divider. But the CD40106B sheet also shows 100mW per output transistor.

 

1. The five inverters are in *parallel*, not series, to increase the current drive capability.

2. The max power dissipation is not an indicator of how the transistor will perform under load. Look at the output high and low output currents, and see that a single output is good for only about 4 mA, and that is with a relatively high voltage drop.

A CMOS output is a medium-impedance voltage source, so multiple outputs in parallel naturally share output currents.

ak

 

Yes to everything. You continue to analyze correctly.

Yes, all capacitors have leakage current, so they all self-discharge. But usually that current is very much lower than whatever signal current is going in/out of the cap. In a timing circuit, the external resistor sets the charge or discharge current only because its resistance is much lower than the capacitor's internal leakage equivalent impedance. This is why long time circuits with a 555 are not recommended. A 12 V circuit with a 1 M resistor has a charging current that peaks at 12 uA and averages less than 4 uA over a cycle. If the leakage current for a multi-hundred uF aluminum electrolytic is 400 nA, that's a 10% error. As a one-off for a home project that's not a problem, just change the resistor value to compensate. But in a production product, no way. Also, the leakage current varies significantly from one cap to another, and with temperature.

I just checked. A low cost 330 uF 25 V cap at Digi-Key has a leakage current of 3 uA (!) or 0.01CV, which ever is greater. 0.01 x 330 Uf x 9 V = 30 uA (!!!). A $1 part brings this down to 16 uA. So, the timing period probably will be noticeably shorter than calculated. That is worse than I thought. Other than forum discussions, I've never actually designed an RC timer for anything over one minute. I've always thought they would suck, but I never ran the numbers to see how badly. Still, others around here swear by them.

Many "hockey-puck" SSR's have a constant-current circuit at the input, so the device draws the same 3 mA (a typical value from memory) for any voltage in the operating range. Thus, 3 mA is the discharge current for the timing cap, and is large enough that no additional resistor is needed. In fact, it is so large that the timing cap is relatively huge. Again, I never would propose this for a commercial product, but for home it is an interesting variation on the theme.

A 24 V transformer has a calculated peak voltage after rectification of over 33 V. Plus your line voltage might be a bit high. Plus the rating is at full load, and this circuit is nowhere near that. The idea is fine, but the transformer secondary should be *rated* at 20 v or less. The circuit already is a large filter capacitor, so all that is needed is one diode.

ak

Damn you and your continued brilliance, incredible dedication to detail, precision evident of a true engineering mind, and blah blah blah blah blah.... While other children were at school delighted over powering a single LED, ak was off in the corner, evaluating the impedance of that LEDs leads, the thermal junction temperature of the stirrup, the lensing parameters of the plastic cover, and questioning privately whether or not that miniscule defect that even the OEM could not detect would make the part unsuitable for his humble night-light project.

Thank you for always sharing so thoroughly and well. There are one of about dozen or so, perhaps a little less, on here that I continually learn from, and I am grateful to each and every one of you for your willingness to share your knowledge, even though sometimes it gets old having to go to so much effort to drive such knowledge into poor minds like mine.

 

No effort at all.

ak was off in the corner,

Actually, I was in the back row of sophmore high school English class. When my mentor died, his wife gave me his entire collection of Popular Electronics. I spent that year digesting 15 years of mags. None of it made sense at first, then some, then more. They taught me; I teach you.

ak

 

Back on subject. I built this several years ago. Has a delayed start so the table saw and vacuum don't start at the same time. Pops a breaker. And added the delay-off on the shop vac. The most of the two halves of the circuit were picked off of Bill Bowden's web page. I posted this on an electronics Forum.

A short time later this came out: https://www.amazon.com/iVAC-10031-010-Automated-Vacuum-Switch/dp/B0035YGLZG

Coincidence?

Ken

 

1. The five inverters are in *parallel*, not series, to increase the current drive capability.

2. The max power dissipation is not an indicator of how the transistor will perform under load. Look at the output high and low output currents, and see that a single output is good for only about 4 mA, and that is with a relatively high voltage drop.

A CMOS output is a medium-impedance voltage source, so multiple outputs in parallel naturally share output currents.

ak

Whoops... I really meant parallel. I'm pretty green in electronics, but I do know the difference.

Okay, I was really reaching trying to find out what the outputs could handle, but I see what you mean now. This hex chip seems pretty well suited to this application.

This weekend hope to get time to hook up the circuit with the oscillator/counter. It's really academic, though. A lot of these circuits would serve my purpose. Fun to try out and learn about something new though!

Thanks.

 

Damn you and your continued brilliance, incredible dedication to detail, precision evident of a true engineering mind, and blah blah blah blah blah.... While other children were at school delighted over powering a single LED, ak was off in the corner, evaluating the impedance of that LEDs leads, the thermal junction temperature of the stirrup, the lensing parameters of the plastic cover, and questioning privately whether or not that miniscule defect that even the OEM could not detect would make the part unsuitable for his humble night-light project.

Thank you for always sharing so thoroughly and well. There are one of about dozen or so, perhaps a little less, on here that I continually learn from, and I am grateful to each and every one of you for your willingness to share your knowledge, even though sometimes it gets old having to go to so much effort to drive such knowledge into poor minds like mine.

Ha ha! That's awesome... quite an image.

Still new here, but I'm already really impressed. Really appreciate the time AK has put into laying out these circuits. And in general, it seems like there's tons of knowledge to be had in the articles and the education section. I'm just scratching the surface so far.

 

Back on subject. I built this several years ago. Has a delayed start so the table saw and vacuum don't start at the same time. Pops a breaker. And added the delay-off on the shop vac. The most of the two halves of the circuit were picked off of Bill Bowden's web page. I posted this on an electronics Forum.
View attachment 147967
A short time later this came out: https://www.amazon.com/iVAC-10031-010-Automated-Vacuum-Switch/dp/B0035YGLZG

Coincidence?
Ken

...or corporate espionage?

Thanks for that idea. I believe I've seen similar on some woodworking forums. I guess everyone has their preferences, and mine it to switch the dust collection on from the blast gates (central DC system). At some point I may consider this kind of switch for shop vacs I have dedicated to certain tools.

 

I built this several years ago. Has a delayed start so the table saw and vacuum don't start at the same time. Pops a breaker. And added the delay-off on the shop vac. The most of the two halves of the circuit were picked off of Bill Bowden's web page. I posted this on an electronics Forum.

Nice use of a pseudo-unijunction transistor. But why have a darlington drive a reed relay that drives a solid-state relay that needs less than 5 mA of input current?

Isn't the start delay R4-C3?

Also, I think the stop delay is R6-C2.

ak

 

I'll just throw in another idea. The hard part is the long time delays. This can be done nicely with a processor.

The triggers could be a voltage or current trigger on the power tool. Current triggers could be integrated into the breaker box for the shop. I/O modules can make isolated voltage connections. You can l find some current detection modules too. You might want to integrate an RF remote.

In any event, the number of tools and how easy to interface is part of the deciding and cost factor.

This http://www.linear.com/product/LTC6995-1 is a 5V only part that could play the role of a low frequency oscillator.

I can look for some I/O modules and current sensors.

The 555 is stupid as timers go. Oscillators, that's different.

This can implement long delays easily.
http://www.airotronics.com/AOTpdfs/multifunction/Airotronics-MC363.pdf

But it's not exactly what you need.

You can gate an oscillator in mode 4 at whatever rate is good. Even say 1 Hz with paralled enable signals from the devices. If the off time is first, it also implements the start delay. This http://www.airotronics.com/products-intervalon.php mentions "delayed interval". I didn't look through the options.

 

The triggers could be a voltage or current trigger on the power tool. Current triggers could be integrated into the breaker box for the shop. I/O modules can make isolated voltage connections. You can l find some current detection modules too. You might want to integrate an RF remote.

There are guys on woodworking forums doing this type of system, not to mention Bob Clagett on his "I Like to Make Stuff" Youtube channel.
My needs are simpler than that. My DC will be only big enough to run for one tool at a time, so I'll need to remember to close blast gates after finished with each tool, and open the next one. That's why I really like the idea of just using switches on the blast gates.
I tend to think a remote is something that will keep getting lost. There are plenty of people who like them; just not for me.

I can find other uses for electronics projects around the shop. Next one might be optical sensors at the doorways so my wife can't sneak up on me while I'm running a board through the tablesaw blade!

 

That's why I really like the idea of just using switches on the blast gates.

That makes sense. It's till applicable to you too.

The suggestion was mainly an idea that combines commercially available large parts interconnected.
Long time delays are difficult to do without a microprocessor.

Without doing anything fancy, the DC and the machine don't come on at the same time.

Here https://www.mouser.com/ds/2/626/IO_Mod_AC_Input-335391.pdf are some example voltage I/O module.

There still can be hiccups when trying to implement it.

 

Nice use of a pseudo-unijunction transistor. But why have a darlington drive a reed relay that drives a solid-state relay that needs less than 5 mA of input current?

Isn't the start delay R4-C3?

Also, I think the stop delay is R6-C2.

ak

AK,

Thanks. You are absolutely right on the timing, and other component labels. I combined two schematics and obviously didn't relabel everything. I think the darlington was left over from driving an electromechanical relay in the early development.

Ken