reducing dc volts with resistor

[rmanbike]

Please help me in figuring the correct size resistor to reduce 2.3 dc volts down to 1.3 dc volts. This is circuit board of a thermostat/thermidistat, which includes a Honeywell HiH-3610 humidity sensor. The documentation for this is here: **broken link removed**.

Background;

The thermostat for my Carrier hvac system has a maxium set point of up to 45%, I would like to increase this to 60%. The only way I can think of to do this is to install a resistor in the output voltage of the humidity sensor to reduce the voltage about 20%.
If this doesnt work I will have to replace the Carrier thermostat for a Honeywell thermostat which has a humidity level set point of up to 60%. But I will loose the functionality of the variable speed/output gas furnace.

 

[betwixt]

What you are asking for is a reasonable solution to the problem but it is impossible to work out the resistor values you need without knowing the surrounding circuit at it's output pin.
Basically you set the divider by working out the ratio of the two resistors as 2.3:1.3 then pick suitable values from what is available but as you add resistance to the output pin of the device it also drops voltage because it is feeding current into the 'load', meaning whatever is connected after the pin. You have to take that extra load into account or the calculation is meaningless.

Brian.

 

[rmanbike]

Voltage input; 5 Vdc 200 μA at 5 Vdc
Voltage output; 0.8 Vdc to 3.9 Vdc output
I could connect a meter to check the voltage at the output to see just how much of a load is put on this sensor, when switching from on to off.
Or anyones best educated guess?

 

[betwixt]

A guess wouldn't be a good idea!

What you could do is use a pre-set potentiometer, connect the sensor output to the top, ground to the bottom and then take the output from the wiper (center) pin. It would work like a volume control in an audio application, you could adjust it to give any voltage less than the sensor produces. As the sensor can only produce a small output current, I would suggest a value of 100K would be suitable.

Brian.

 

[rmanbike]

Ok, I like your idea, Brian! So I would only need to cut just the connection from the center pin (out) of the sensor to the circuit board.
I see 3 terminals 1 - 2 - 3 . On a potentiometer
Then wire:
Terminal 1 (top) solder to the output of the sensor.
Terminal 3 (bottom) to ground side of sensor.
Terminal 2 (center) to the circuit board input, that was previously the input from the sensor (center pin).

What you could do is use a pre-set potentiometer, connect the sensor output to the top, ground to the bottom and then take the output from the wiper (center) pin. It would work like a volume control in an audio application, you could adjust it to give any voltage less than the sensor produces. As the sensor can only produce a small output current, I would suggest a value of 100K would be suitable.

Brian.[/QUOTE]

 

[betwixt]

That is correct. The control should let you adjust how much of the original sensor voltage is passed to your circuit board. You can turn the control until you see 1.3V going to your board.

Brian.

 

[rmanbike]

Thanks "It works like a charm" got comfortable heat & some humidity now!

 

[paulmdrdo]

panget mo.