Yeah I agree but you figure the first printing was in 1982. So yes, it is an old design. I suggested newer parts but to get across the idea using DTMF I suggested using Audacity as a tone generator and see about getting a 567 decoder to respond. I ran the ancient 741 chip off of +/- 9 volt battery supplirs. long enough to know they work.

I figure we see what thread starter comes back with..

Ron

 

And I suspect that DTMF, op amp selection, etc... may be beyond the TS pay grade, given the presentation of the original design.

The TX/RX 433MHz modules are an excellent suggestion.

Agreed, I already ordered these modules and I'll figure the rest out when I get them.

 

The 433 MHz module is not for continuous use! It is for intermittent signalling only. Continuous transmission is explicitly outlawed in the United States Code of Federal Regulations (CRF Title 47 if memory serves). Other countries have similar restrictions for this frequency.

Some people will recall a story in the news about two years ago in which people in a certain area could not unlock their cars -somebody in the neighborhood has set up a 433 MHz tx and rx as part of a burglar alarm and it was jamming the frequency day and night. It was days before they found him and people were able live "normally" again.

 

The 433 MHz module is not for continuous use! It is for intermittent signalling only. Continuous transmission is explicitly outlawed in the United States Code of Federal Regulations (CRF Title 47 if memory serves). Other countries have similar restrictions for this frequency.

Some people will recall a story in the news about two years ago in which people in a certain area could not unlock their cars -somebody in the neighborhood has set up a 433 MHz tx and rx as part of a burglar alarm and it was jamming the frequency day and night. It was days before they found him and people were able live "normally" again.

The tramsmitter does not stay on the air, it transmits pulses of data. It is also not going to be continuous duty, since it will only be when the kart is in operation. Additionally, it's ERP will be extremely limited.

All irrelevant, there is a rule in 10CFR47 Part 15.231 that limits on air time to 2 seconds per hour which makes a solution using the cheap modules expensive and not as simple. Sorry I missed that and thanks for @DickCappels for catching it.

 

The 433 MHz module is not for continuous use! It is for intermittent signalling only. Continuous transmission is explicitly outlawed in the United States Code of Federal Regulations (CRF Title 47 if memory serves). Other countries have similar restrictions for this frequency.

Some people will recall a story in the news about two years ago in which people in a certain area could not unlock their cars -somebody in the neighborhood has set up a 433 MHz tx and rx as part of a burglar alarm and it was jamming the frequency day and night. It was days before they found him and people were able live "normally" again.

Checking 10CFR47 Part 15.231 I find that you are correct insofar as the limit is 2 seconds per hour. To do that with these modules will require MCUs on both ends. This is not a good solution for the TS.

I'm sorry I missed this particular regulation which makes the solution not a solution at all. The only service this leaves is RCRS and that does actually specifically permit this use:

30 channels (75.4 – 76.0 MHz) are available for model surface craft devices. These devices include any small imitation of a boat, car or vehicle for carrying people or objects, except aircraft.

Now I have to find cheap hardware for this band.

Thanks for catching that, Dick.

 

Well, not having a lot of luck with the RCRS service but here's something that would work though it is a little on the overkill side:

https://www.amazon.com/dp/B07PKNVZZ9/

These 2.4GHz systems are very common, lots of choices. Right now it's the only option I can find. I will look more for RCRS 74Mhz stuff when I get the chance but it seems that will be much more expensive.

 

Can the 433MHz be pulsed once every second (or similar small delta) with a 555 circuit? Then the RX module can trigger a retriggerable timer delay relay (such as the one linked). If the receiver doesn’t receive a “heartbeat” signal every time period, the relay will open, cutting power to the kart.

I think this protocol could keep the TX/RX time under 2 seconds every hour, satisfying the regulation.

And it doesn’t require an MCU.

 

Can the 433MHz be pulsed once every second (or similar small delta) with a 555 circuit? Then the RX module can trigger a retriggerable timer delay relay (such as the one linked). If the receiver doesn’t receive a “heartbeat” signal every time period, the relay will open, cutting power to the kart.

I think this protocol could keep the TX/RX time under 2 seconds every hour, satisfying the regulation.

And it doesn’t require an MCU.

Yes, but it also makes the safety feature less safe. You'd have to assert positive control (with another of the channels) to stop, or if that failed, count on the lack of the watchdog ping but that would be 2 seconds away which could be an eternity in kart time.

I was thinking that MCU (very simple ones) on each end would be best, but same idea with the same problem. Now if you could rely on the positive control, you could use a supervisory ping that way. I don't know if the TS would be willing to do that as opposed to the immediate failsafe.

 

Yes, but it also makes the safety feature less safe. You'd have to assert positive control (with another of the channels) to stop, or if that failed, count on the lack of the watchdog ping but that would be 2 seconds away which could be an eternity in kart time.

I was thinking that MCU (very simple ones) on each end would be best, but same idea with the same problem. Now if you could rely on the positive control, you could use a supervisory ping that way. I don't know if the TS would be willing to do that as opposed to the immediate failsafe.

Fair enough. I didn’t do the math, but I expect transmittal over one channel to take far less than one second. If the ratio of on/off times is less than 1/1800, the regs will be satisfied.

Assuming that a key code is 8 bits (could be as small as two bits to encode four channels) and given the modules transmit at 10kB/s, sending one key code will take 0.0008 seconds. Which if pulsed at 1Hz, will take 2.88 seconds.

Does not meet regulation However a five bit or less key code would!

Or, another approach is to pulse at less than 1Hz. Once every (rounded up) 1.5s would meet regs. But as you say, that’s an eternity in the cart world.

So, we’d need to confirm what the key code length is. Or find a module that transmits faster than 10kB/s.

 

Fair enough. I didn’t do the math, but I expect transmittal over one channel to take far less than one second. If the ratio of on/off times is less than 1/1800, the regs will be satisfied.

Assuming that a key code is 8 bits (could be as small as two bits to encode four channels) and given the modules transmit at 10kB/s, sending one key code will take 0.0008 seconds. Which if pulsed at 1Hz, will take 2.88 seconds.

Does not meet regulation However a five bit or less key code would!

Or, another approach is to pulse at less than 1Hz. Once every (rounded up) 1.5s would meet regs. But as you say, that’s an eternity in the cart world.

So, we’d need to confirm what the key code length is. Or find a module that transmits faster than 10kB/s.

I ordered some of these. I’ll get them Friday.

 

Rats -only 2 seconds/hour. There goes my telemetry setup!

 

Wow, I just gave this a read: Using 433 MHz for wireless connectivity in the Internet of Things. I was not aware of all of the restrictions imposed. The US Federal Communications Commission (FCC) regulates operation at 433 MHz under Regulation 10CFR47 Part 15.231. I have over the last few years played around with a few of these:
INSMA 433Mhz Wireless RF Switch Long Range DC 12V 4CH Channel Wireless Remote Control Switch, DC12V Relay Receiver Module, Transmitter Toggle Switch RF Relay (2 Transmitter & 1 Receiver) . They can be setup for momentary or latching operation. Again, never gave any thought to the restrictions.

Finally early on my goal was merely to show the thread starter how DTMF could be used. I suggested off the shelf modules which require no in depth knowledge of electronics. Complete modules are available and inexpensive.

Ron

 

Wow, I just gave this a read: Using 433 MHz for wireless connectivity in the Internet of Things. I was not aware of all of the restrictions imposed. The US Federal Communications Commission (FCC) regulates operation at 433 MHz under Regulation 10CFR47 Part 15.231. I have over the last few years played around with a few of these:
INSMA 433Mhz Wireless RF Switch Long Range DC 12V 4CH Channel Wireless Remote Control Switch, DC12V Relay Receiver Module, Transmitter Toggle Switch RF Relay (2 Transmitter & 1 Receiver) . They can be setup for momentary or latching operation. Again, never gave any thought to the restrictions.

Finally early on my goal was merely to show the thread starter how DTMF could be used. I suggested off the shelf modules which require no in depth knowledge of electronics. Complete modules are available and inexpensive.

Ron

You still have to transmit and receive the DTMF signals and that's the rub. Which service/band do you propose?

 

I have no clue as to distance? Knowing what I know now, I see no need for DTMF or even tones. My first choice would likely be the 433 MHz module I linked to but less knowing distance and terrain I can't really come up with a good answer. Depending on the area another option might be something WiFi. It seems all the thread starter wants is a remote kill switch for a Go Kart? Things have good better with a good explanation and I agree based on skill level a modular solution would be a good thing. If the area is WiFi enabled I have been using a few of these smart 12 VDC cards and I can turn them on and off using my smart phone from anywhere. I can also tell Alexa to turn them on and off.

Ron

 

I have no clue as to distance? Knowing what I know now, I see no need for DTMF or even tones. My first choice would likely be the 433 MHz module I linked to but less knowing distance and terrain I can't really come up with a good answer. Depending on the area another option might be something WiFi. It seems all the thread starter wants is a remote kill switch for a Go Kart? Things have good better with a good explanation and I agree based on skill level a modular solution would be a good thing. If the area is WiFi enabled I have been using a few of these smart 12 VDC cards and I can turn them on and off using my smart phone from anywhere. I can also tell Alexa to turn them on and off.

Ron

That module is very much like the one already ordered by the TS. The problem is, he wants a deadman switch to shut down a mini go kart for the safety of children. He wants to have it cut the power if he lets go or the kart goes too far away.

The required transmissions exceed the regulatory limits.

 

That module is very much like the one already ordered by the TS. The problem is, he wants a deadman switch to shut down a mini go kart for the safety of children. He wants to have it cut the power if he lets go or the kart goes too far away.

The required transmissions exceed the regulatory limits.

That is not a bad question! How far away from the TS is he expecting the cart to travel?

Perhaps a hacked 2.4GHz RC Car could’ve used in a modular approach. Just use the motor leads to power a relay. The relay switches power to the kart.

Failsafe... if the receiver loses signal or its batteries die, the kart stops. To prevent against accidental operation, use the toys steering or reverse functions in series so that two functions need to be activated.

I just don’t know if the 2.4GHz band provides the appropriate distance. Give me a while to look that up.

 

That is not a bad question! How far away from the TS is he expecting the cart to travel?

Perhaps a hacked 2.4GHz RC Car could’ve used in a modular approach. Just use the motor leads to power a relay. The relay switches power to the kart.

Failsafe... if the receiver loses signal or its batteries die, the kart stops. To prevent against accidental operation, use the toys steering or reverse functions in series so that two functions need to be activated.

I just don’t know if the 2.4GHz band provides the appropriate distance. Give me a shoot to look that up.

A few posts up I linked a 2.4GHz remote control car controller and board as an alternative. Not too expensive but more than is needed.

He said he didn't want it to go very far.

 

A few posts up I linked a 2.4GHz remote control car controller and board as an alternative. Not too expensive but more than is needed.

He said he didn't want it to go very far.

Sorry I missed that.

He could always buy a cheep (<$20) RC Car and try it out where he expects to operate the kart...

 

That module is very much like the one already ordered by the TS. The problem is, he wants a deadman switch to shut down a mini go kart for the safety of children. He wants to have it cut the power if he lets go or the kart goes too far away.

The required transmissions exceed the regulatory limits.

OK, now I got it. He wants to hold a button allowing the Kart to run and have the Kart stop on button release. I was thinking latch and unlatch. Where a few millisecond pulse latches or unlatches. Well my bad on that note. While too far away is hard to define releasing a button is easy enough to grasp. Maybe hacking a walkie talkie is not a bad idea?

Ron

 

OK, now I got it. He wants to hold a button allowing the Kart to run and have the Kart stop on button release. I was thinking latch and unlatch. Where a few millisecond pulse latches or unlatches. Well my bad on that note. While too far away is hard to define releasing a button is easy enough to grasp. Maybe hacking a walkie talkie is not a bad idea?

Ron

And back to the problem of legality. Such a use is strictly prohibited by Part 95, unfortunately.