Hi i have a tractor mounted potato planter with a belt feed indicator control box which the led is not working on one side.
In essence the system is 12 v, it has 2 proximity switches to sense potatoes on the belt when there is none it will trigger the light in the cab box and after a delay of 1 to 3 seconds (adjustable) if the light is still on it will activate a buzzer.
I have contacted the manufacturer and due to its age no parts are now available.
My question is and i almost think it could be simple although i could find out otherwise is, if i were to remove the old non working simple PCB and use the two trigger wires from the 2 proximity switches to supply 2 individual panel mounted LED lights and put some sort of timer relay in the circuitry alongside the lights and protect them each with a diode to stop the unlit light from being activated after the required delay the buzzer would activate. Does anyone think this could work and is there any recommendations for a time delay relay or similar ? Many thanks.

 

If you posted really good pictures of the parts and top and bottom of board.

Maybe able to walk you thew fixing it. Or how to make new one.

 

If you posted really good pictures of the parts and top and bottom of board.

Maybe able to walk you thew fixing it. Or how to make new one.

 

Hi thanks for the reply i will take some photos of the board tomorow. I have drawn a rough scetch of what i think may work dont know if you got it.

 

With agricultural kit the most likely cause of failure is a broken connection or corrosion, especially if animals have been able to chew it, kick it or crap on it. Worth checking for such mechanical issues before building a new unit.

 

With agricultural kit the most likely cause of failure is a broken connection or corrosion, especially if animals have been able to chew it, kick it or crap on it. Worth checking for such mechanical issues before building a new unit.

Thanks but it only lives indoors and away from animals and i have metered and tested everything to come to this conclusion.

 

Thanks but it only lives indoors and away from animals and i have metered and tested everything to come to this conclusion.

Your tractor mounted potato planter only lives indoors? Do you plant enough indoor potatoes to need a tractor for the job? Are there massive potato greenhouses somewhere?

 

Thanks but it only lives indoors and away from animals and i have metered and tested everything to come to this conclusion.

The circuit should not be very complex, and so it ought to be repairable. But as others have already commented, the very first thing to check is the external connections. First, verify that both the 12 volts and the common connection are actually present on the board, then next, verify that the switch connections are good on the board. To check the switch connections use a voltmeter to read the voltage across the switch connection, it should be zero with the switch closed and closer to 12 volts with the switch open. If it never changes then either the switch is failed or there is a bad connection in the wire some place, or the wire may be short-circuited if the voltage stays at zero. If neither side works then my guess is that the problem is in the power feed, or, both indicator lights have failed.

 

Your tractor mounted potato planter only lives indoors? Do you plant enough indoor potatoes to need a tractor for the job? Are there massive potato greenhouses somewhere?

It plants outdoors as standard. After 35 years of agricultural engineering including all mechanical and electrical fault finding i know exactly what is wrong with it just need some usefull advice to repair or knock up an alternative with some led panel lamps an off the shelf 0-10 sec timer relay and some diodes to eliminate backfeed to the other lamp.

 

If you know exactly what is wrong with it then if you tell us what it is we may be able to help you source the faulty part.

Les.

 

It plants outdoors as standard. After 35 years of agricultural engineering including all mechanical and electrical fault finding i know exactly what is wrong with it just need some usefull advice to repair or knock up an alternative with some led panel lamps an off the shelf 0-10 sec timer relay and some diodes to eliminate backfeed to the other lamp.

Sorry if my earlier comment came off as snarky. I didn't mean to offend you or question your assessment of things thus far.

As @LesJones suggested, if you know exactly what's wrong, why not tell us what the problem is? Do you just mean that you've already tested switches, switch wires, and power wires and you're sure that the problem is in the PCB?

Assuming you've already checked everything else and you're sure the problem is in the PCB, then the next step is probably getting those good front/back pics of the PCB.

 

Hi thanks for the reply i will take some photos of the board tomorow. I have drawn a rough scetch of what i think may work dont know if you got it.

Regarding the sketch, I think the basic concepts look right.

I always mix up the terminology on the various kinds of timer delays, but you should have no problem finding an existing encapsulated timer that does what you want, or you can make your own timer with a 555 or 4060 based circuit.

Two possible issues I see:

• I think you've got the diodes oriented backwards.
• We need to know more about the switches. You've drawn them as if they're mechanical switches, in which case they would almost certainly be rated for enough current to directly power the LED panel lights and provide a timer trigger signal. However, when you say "proximity switch," that makes me think of optical interrupters, capacitive or ultrasound proximity switches, etc. Many of those switches output a high impedance signal voltage which would not be suitable for powering anything. Depending on the actual nature of your switches, you might need an input buffer stage between the switches and the LEDs/timer inputs.

 

If you know exactly what is wrong with it then if you tell us what it is we may be able to help you source the faulty part.

Les.

If the lights still blink as the switches operate then I can design you a really simple circuit. My guess is that you want to replace incandescent lights with LED devices to avoid the failed lights syndrome. You can use high brightness LEDs and they can also serve as the isolation diodes to charge a capacitor to keep the buzzer control transistor cut off. One or two transistors and an electronic buzzer plus the capacitor would be the system. I can't deliver the circuit drawing today but does that sound simple enough? I don't know what part of the world you are in so I don't know what parts would be simple to get and what parts are not available. Knowing available parts will help get the design buildable the first time.

 

Regarding the sketch, I think the basic concepts look right.

I always mix up the terminology on the various kinds of timer delays, but you should have no problem finding an existing encapsulated timer that does what you want, or you can make your own timer with a 555 or 4060 based circuit.

Two possible issues I see:

• I think you've got the diodes oriented backwards.
• We need to know more about the switches. You've drawn them as if they're mechanical switches, in which case they would almost certainly be rated for enough current to directly power the LED panel lights and provide a timer trigger signal. However, when you say "proximity switch," that makes me think of optical interrupters, capacitive or ultrasound proximity switches, etc. Many of those switches output a high impedance signal voltage which would not be suitable for powering anything. Depending on the actual nature of your switches, you might need an input buffer stage between the switches and the LEDs/timer inputs.

Thanks i agree looking again i have in my haste drawn the diodes the wrong way round. The circuitry is very basic and all the switching uses 12 v its only the pcb that uses a lower voltage for the led's and the output to the buzzer is again 12 v

 

Sorry if my earlier comment came off as snarky. I didn't mean to offend you or question your assessment of things thus far.

As @LesJones suggested, if you know exactly what's wrong, why not tell us what the problem is? Do you just mean that you've already tested switches, switch wires, and power wires and you're sure that the problem is in the PCB?

Assuming you've already checked everything else and you're sure the problem is in the PCB, then the next step is probably getting those good front/back pics of the PCB.

 

The control box is a generic box for up to 3 rows and ours is only a 2 row which is why you will notice there are three led lamps, so i dont need everything thats there.

 

Can you provide the following information. What is the part number of the IC ? (The picture is not clear enough to read it.)
What are the parts numbers on the transistors ?
Can you tell us which colour wires come from each sensor, which colour wires go to the buzzer and what colour wires are the power supply wires ?
What is the nature of the output of the proxomity sensors ? (Switch contacts, logic level, open collector or something else.)
On the side with the LED that is not working does the buzzer still sound after a time if there are no potatoes on that side ?

Les.

 

Judging by the sticky tape and view of the underside of the board it looks as though someone has already had a go at a modification?

 

Judging by the sticky tape and view of the underside of the board it looks as though someone has already had a go at a modification?

Someone has been in to it before, i agree not sure why, it is 23 years old so there will be some history it looks like a couple of resistors have been added although cant be sure, the manufacturers are unable to help much as they upgraded the inside of the control box in 1997 and again since although they are helpful none of their factory or mobile service engineers have any parts left or any schematics now. So now unless i want to part with large sum's of money for their latest control box for the machine and the tractor i need a simple solution.

 

If the lights still blink as the switches operate then I can design you a really simple circuit. My guess is that you want to replace incandescent lights with LED devices to avoid the failed lights syndrome. You can use high brightness LEDs and they can also serve as the isolation diodes to charge a capacitor to keep the buzzer control transistor cut off. One or two transistors and an electronic buzzer plus the capacitor would be the system. I can't deliver the circuit drawing today but does that sound simple enough? I don't know what part of the world you are in so I don't know what parts would be simple to get and what parts are not available. Knowing available parts will help get the design buildable the first time.