Help with servo current limiter on Snoopy's Robot boat

[Robin Lovelock on robin@gpss.co.uk]

Hi Guys. This just sent to Picaxe Forum who have provided the most expert advice so far ...

Hi Guys. I just googled "5v automatic switch off if 5v voltage low" and the AI Overview said what I was looking for, between Picaxe 28X2 computer and servo. BUT, looking at the details of various low cost products, I did not see the important information. What I think the need is: switch OFF the red power lead if voltage drops below a threshold. e.g. 4.0v. AND only switch back on if above a higher voltage threshold. e.g. 5.0v. Why ? Because I think that it would go into an osculation. i.e. when below a single threshold, like 4.5v, switching off the (stalled) servo load would result in the voltage rising quickly again. This is reflected on all the tests on Snoopy's Robot Boat in our front garden. All documented in detail, including pictures, videos, and voltages, on "Blog11" on www.gpss.co.uk/rbblog11.htm Take Care. Robin. www.gpss.co.uk & Snoopy on www.gpss.co.uk/autop.htm

[Philip Smith]

Robin,

You might find something that is designed to cut off a battery when the voltage goes below a certain value: this would be for Lithium batteries, so the cut off for 1 cell might be about 3V (or perhaps down to 2.5) and for 2 cells double these. So, perhaps, there will be something close enough to what you want for a 2 cell battery. This might match up with the battery you have for your boat if it is a 2 cell lithium. Look up "2s battery protection" on Ebay for example. I must admit it isn't clear to me exactly how you would use the ones on Ebay, but I think they should be able to do the job somehow. And they're cheap so you can experiment.

Otherwise you have the choice of making a circuit to do it, using perhaps an op-amp, a voltage reference and a transistor. Alternatively, use an analogue input to your Picaxe (If it has any, I don't know anything about the pickaxe), and use an output to turn on and off a transistor. I actually turn on and off a voltage regulator with an enable instead of a simple transistor as the regulator has useful features such as overcurrent protection.

Phil

[Robin Lovelock on robin@gpss.co.uk]

Thanks Pierce & Phil. Sorry if http://www.gpss.co.uk/rbblog11.htm is not clearer.

More in a moment, but Alistair, in Belgium, regular visits the page above to see if updated.

I'm guessing Phil would come up as "Cambridge", and last visit seems to be last Sunday.

I come up as "Redhill" even if Sunninghill, Ascot, nowhere near Redhill :-)

I've just made a minor update, but no change: boat left on waiting for sunlight.

Now - what I hope should be clear:  I am using a standard off-the-shelf servo,

and standard Picaxe servo driving, with software unchanged since December 2017.

What I'm looking for is ideally simply put in between Picaxe and Servo.

i.e. same as if were using a standard radio control receiver - > servo.

Ideally advice, as from Buzby on Picaxe forum, who had actually tried to do something similar.

Variations are obviously possible, such as an extra input from the solar power source,

or maybe a reed relay detecting that the servo has come close to, or reached the "stop".

I am reminded of that expression coined by that brilliant avionics engineer ...

KISS = Keep It Simple, Stupid ;-)

It's quite useful to know if guy's browsers are hiding visit, but very useful to see when someone looked at a page.

Guys feedback often tells me to add something to make it clearer.

Sorry for delay - just back from birthday pub lunch with 3 local friends, celebrating an 88th birthday.

My card to him included a cartoon of two fat ladies. More importantly, the pub made a special cake

inspired by the "Under Siege Cake Scene". Naa - not full sized, but a barbie doll ;-)

https://www.youtube.com/watch?v=m5Py6DmSe58 ;-)

Take Care

Robin

http://www.gpss.co.uk

On Thursday, October 31, 2024 at 03:33:10 PM GMT, Pierce Nichols <pierce...@gmail.com> wrote:

Assuming you have an analog input on the Picaxe to measure system voltage, there are several ways to implement a high-side power switch.

I like Infineon's IPS series of intelligent power switches, but they generally require a load voltage over 5.5V in order to work reliably. They include nice things like overcurrent protection and they're not terribly expensive. One switch to rule them all, more or less.

You can use a logic level N-channel MOSFET to drive the gate of a P-channel MOSFET and use that to switch the high side. This requires three parts rather than one (the two MOSFETs plus a pull-up resistor on the gate of the PMOS) but is certainly the cheapest option.

Vishay makes a part called the VOM1271, which is an optoisolator with a tiny photovoltaic cell designed to drive the gate of an N-channel MOSFET in a high side configuration.

-p

On Tue, Oct 29, 2024 at 5:54 AM 'Robin Lovelock on ro...@gpss.co.uk' via Microtransat <microt...@googlegroups.com> wrote:

Hi Guys. This just sent to Picaxe Forum who have provided the most expert advice so far ...

Hi Guys. I just googled "5v automatic switch off if 5v voltage low" and the AI Overview said what I was looking for, between Picaxe 28X2 computer and servo. BUT, looking at the details of various low cost products, I did not see the important information. What I think the need is: switch OFF the red power lead if voltage drops below a threshold. e.g. 4.0v. AND only switch back on if above a higher voltage threshold. e.g. 5.0v. Why ? Because I think that it would go into an osculation. i.e. when below a single threshold, like 4.5v, switching off the (stalled) servo load would result in the voltage rising quickly again. This is reflected on all the tests on Snoopy's Robot Boat in our front garden. All documented in detail, including pictures, videos, and voltages, on "Blog11" on www.gpss.co.uk/rbblog11.htm Take Care. Robin. www.gpss.co.uk & Snoopy on www.gpss.co.uk/autop.htm

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[Francis Roussel]

Bonjour Phil,

En attendant de poursuivre cet hiver mes préparatifs pour avoir un voilier autonome, le problème de l'alimentation (ou pas) est un souci qu'il faut résoudre si on ne veut pas perdre son bateau.

Une alimentation solaire permet de recharger ses batteries, oui mais le soleil n'est pas toujours présent et les batteries peuvent se décharger.

En utilisant un https://fr.aliexpress.com/w/wholesale-ka75330.html dont la sortie est connectée au reset de mon ESP32 dès que la tension passe en dessous de 3,3V le microcontrôleur est bloqué

Donc un BMS pour couper l'accumulateur quand il descend et un KA pour ne laisser démarrer le ESP32 quand la tension remonte semble être bien mais il n'y a pas assez d'hystérésis , l'ESP va tirer au démarrage pas mal sur l'accumulateur et celui-ci va re-déclencher le BMS voire l'ESP démarre mal et c'est fichu il faut un reset manuel, lequel est impossible en pleine mer.

N'ayant pas trouvé un composant comme le KA en vente à l'unité ou presque mais avec un hystérises plus grand, j'ai contourné le problème : le KA sert à bloquer un digispark qui mesure la tension de l'accu, il demande peu de courant et fonctionne à une tension bien plus basse que 3,3v.
Quand il mesure une tension de l'accumulateur au-dessus de 3,6v, on est sûr que l'accu est chargé. Le digispark rétablit l'alimentation de l'esp et du reste de l'équipement avec un Mosfet P.

Cordialement
fr

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[Pierce Nichols]

Assuming you have an analog input on the Picaxe to measure system voltage, there are several ways to implement a high-side power switch.

I like Infineon's IPS series of intelligent power switches, but they generally require a load voltage over 5.5V in order to work reliably. They include nice things like overcurrent protection and they're not terribly expensive. One switch to rule them all, more or less.

You can use a logic level N-channel MOSFET to drive the gate of a P-channel MOSFET and use that to switch the high side. This requires three parts rather than one (the two MOSFETs plus a pull-up resistor on the gate of the PMOS) but is certainly the cheapest option.

Vishay makes a part called the VOM1271, which is an optoisolator with a tiny photovoltaic cell designed to drive the gate of an N-channel MOSFET in a high side configuration.

-p

On Tue, Oct 29, 2024 at 5:54 AM 'Robin Lovelock on ro...@gpss.co.uk' via Microtransat <microt...@googlegroups.com> wrote:

Hi Guys. This just sent to Picaxe Forum who have provided the most expert advice so far ...

Hi Guys. I just googled "5v automatic switch off if 5v voltage low" and the AI Overview said what I was looking for, between Picaxe 28X2 computer and servo. BUT, looking at the details of various low cost products, I did not see the important information. What I think the need is: switch OFF the red power lead if voltage drops below a threshold. e.g. 4.0v. AND only switch back on if above a higher voltage threshold. e.g. 5.0v. Why ? Because I think that it would go into an osculation. i.e. when below a single threshold, like 4.5v, switching off the (stalled) servo load would result in the voltage rising quickly again. This is reflected on all the tests on Snoopy's Robot Boat in our front garden. All documented in detail, including pictures, videos, and voltages, on "Blog11" on www.gpss.co.uk/rbblog11.htm Take Care. Robin. www.gpss.co.uk & Snoopy on www.gpss.co.uk/autop.htm

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