Smile, for you are doing a good deed.

This was what a group of life sciences and chemical technology students at Ngee Ann Polytechnic (NP) told some 50,000 strangers last month, as part of a campaign to raise funds for two charities - the St John's Home for Elderly Persons and Xin Yuan Community Care.

About 800 students went around Singapore, covering areas such as Chinatown, Bugis and Jurong, approaching strangers to smile for a photograph.

Each smile collected $1, split between the two charities.

Mr Scottz Lip, 38, who lectures at NP's school of life sciences and chemical technology, said: "We thought of the idea of a smile campaign because it symbolises gratitude.

"It is to thank our pioneer generation, and also to remind ourselves to be thankful for what we have that others may not have."

It was in this spirit that the two beneficiaries, which help needy old folks, were chosen.

The students raised $80,600 for the charities through the campaign.

This was mostly donated by the polytechnic's industry partners, including pharmaceutical and biotech firm Lonza. A portion of the money qualified for a grant from the Government.

In addition, NP also gave part of the $150,000 that it received from the Ministry of Education under the SG50 Giving initiative to the two charities.

Under the initiative, primary and secondary schools, junior colleges, the polytechnics and the Institute of Technical Education were each given a sum of money to help their chosen charities.

Student Sheetal Bharadwaj, 19, who participated in the campaign, had set up a booth in NP to collect smiles from students.

"A lot of people were willing to do it once they knew that it was for charity, and they would raise $1," she said.

Fellow schoolmate Sharifah Yasmeen, 19, a landscape design and horticulture student, agreed. She had gone to Bugis to canvass for smiles with her classmates.

She recalled: "I didn't experience a lot of rejections. The people were quite friendly in general. As we approached them, we also told them about the two beneficiaries."

Students from the same school also took a group of 40 old folks out on an excursion to places of heritage around Singapore.

They also organised a donation drive to collect food items for needy families.

Separately, students from NP's mechanical engineering school developed a smart toilet sensor for Ren Ci Community Hospital.

The device is designed to make it easier for caregivers to track the patients' movements in the toilet.

An elderly person who is facing difficulties while in a toilet in the hospital would have to yank an emergency pull cord to alert someone outside for help.

"But the pull cord system is a passive one which requires the patient to be conscious enough to pull it," said NP lecturer Edwin Ho, who is also a senior manager at the polytechnic's automation and system centre.

His students made a smart toilet sensor that measures the distance from the toilet seat cover to the patient's back.

Any change in the distance would mean that the patient is moving. This would then sound an alarm to alert the caregiver outside.

The project, which started in 2012, is now in its final stage and the polytechnic has inked a deal to allow a firm to produce the sensors for the mass market.

Ms Regina Ng, deputy director of the mechanical engineering school, said NP plans to use a portion of its SG50 Giving fund to purchase up to 10 sets of the sensors for Ren Ci Community Hospital.

"Ren Ci is currently using prototypes of the sensor," she said.

"Through this project, students also learn about the community spirit of helping one another."